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 $114.38   8.562%   $124.1732   $124.17   $124.15   $124.20  
  Purchase #2 $68.74   7.540%   $73.923   $73.92   $73.90   $73.90  
  Purchase #3 $61.35   4.837%   $64.3175   $64.32   $64.30   $64.30  
  Purchase #4 $192.72   9.153%   $210.3597   $210.36   $210.35   $210.40  
  Purchase #5 $204.60   13.515%   $232.2517   $232.25   $232.25   $232.30  
  Purchase #6 $151.88   7.800%   $163.7266   $163.73   $163.75   $163.70  
  Purchase #7 $132.37   8.536%   $143.6691   $143.67   $143.65   $143.70  
  7 purchase totals = $926.04       $1,012.4208   $1,012.42   $1,012.35   $1,012.50