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 $64.43   13.272%   $72.9811   $72.98   $73.00   $73.00  
  Purchase #2 $165.79   13.779%   $188.6342   $188.63   $188.65   $188.60  
  Purchase #3 $132.92   13.828%   $151.3002   $151.30   $151.30   $151.30  
  Purchase #4 $238.43   3.500%   $246.7751   $246.78   $246.80   $246.80  
  Purchase #5 $128.52   11.330%   $143.0813   $143.08   $143.10   $143.10  
  Purchase #6 $191.50   7.381%   $205.6346   $205.63   $205.65   $205.60  
  Purchase #7 $38.66   4.484%   $40.3935   $40.39   $40.40   $40.40  
  7 purchase totals = $960.25       $1,048.8000   $1,048.79   $1,048.90   $1,048.80