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 $241.62   8.781%   $262.8367   $262.84   $262.85   $262.80  
  Purchase #2 $21.62   6.428%   $23.0097   $23.01   $23.00   $23.00  
  Purchase #3 $225.39   12.103%   $252.669   $252.67   $252.65   $252.70  
  Purchase #4 $48.37   3.205%   $49.9203   $49.92   $49.90   $49.90  
  Purchase #5 $113.39   12.594%   $127.6703   $127.67   $127.65   $127.70  
  Purchase #6 $159.42   8.146%   $172.4064   $172.41   $172.40   $172.40  
  Purchase #7 $207.73   8.331%   $225.036   $225.04   $225.05   $225.00  
  7 purchase totals = $1,017.54       $1,113.5484   $1,113.56   $1,113.50   $1,113.50