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 $207.79   5.252%   $218.7031   $218.70   $218.70   $218.70  
  Purchase #2 $244.57   4.551%   $255.7004   $255.70   $255.70   $255.70  
  Purchase #3 $164.34   12.562%   $184.9844   $184.98   $185.00   $185.00  
  Purchase #4 $7.27   4.567%   $7.602   $7.60   $7.60   $7.60  
  Purchase #5 $222.70   13.227%   $252.1565   $252.16   $252.15   $252.20  
  Purchase #6 $246.58   9.771%   $270.6733   $270.67   $270.65   $270.70  
  Purchase #7 $86.94   9.755%   $95.421   $95.42   $95.40   $95.40  
  7 purchase totals = $1,180.19       $1,285.2407   $1,285.23   $1,285.20   $1,285.30