Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.72   9.231%   $264.0332   $264.03   $264.05   $264.00  
  Purchase #2 $226.74   5.654%   $239.5599   $239.56   $239.55   $239.60  
  Purchase #3 $163.42   6.343%   $173.7857   $173.79   $173.80   $173.80  
  Purchase #4 $151.97   13.691%   $172.7762   $172.78   $172.80   $172.80  
  Purchase #5 $200.87   6.655%   $214.2379   $214.24   $214.25   $214.20  
  Purchase #6 $163.28   13.343%   $185.0665   $185.07   $185.05   $185.10  
  Purchase #7 $214.36   8.668%   $232.9407   $232.94   $232.95   $232.90  
  7 purchase totals = $1,362.36       $1,482.4001   $1,482.41   $1,482.45   $1,482.40