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 $201.88   6.636%   $215.2768   $215.28   $215.30   $215.30  
  Purchase #2 $204.94   4.325%   $213.8037   $213.80   $213.80   $213.80  
  Purchase #3 $210.56   4.318%   $219.652   $219.65   $219.65   $219.70  
  Purchase #4 $64.97   4.361%   $67.8033   $67.80   $67.80   $67.80  
  Purchase #5 $182.66   10.323%   $201.516   $201.52   $201.50   $201.50  
  Purchase #6 $140.29   8.158%   $151.7349   $151.73   $151.75   $151.70  
  Purchase #7 $164.50   5.523%   $173.5853   $173.59   $173.60   $173.60  
  7 purchase totals = $1,169.80       $1,243.3720   $1,243.37   $1,243.40   $1,243.40