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 $57.66   8.194%   $62.3847   $62.38   $62.40   $62.40  
  Purchase #2 $222.98   9.365%   $243.8621   $243.86   $243.85   $243.90  
  Purchase #3 $204.68   6.651%   $218.2933   $218.29   $218.30   $218.30  
  Purchase #4 $79.86   8.263%   $86.4588   $86.46   $86.45   $86.50  
  Purchase #5 $78.66   12.404%   $88.417   $88.42   $88.40   $88.40  
  Purchase #6 $74.98   12.195%   $84.1238   $84.12   $84.10   $84.10  
  Purchase #7 $212.99   6.497%   $226.828   $226.83   $226.85   $226.80  
  7 purchase totals = $931.81       $1,010.3677   $1,010.36   $1,010.35   $1,010.40