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 $48.98   4.298%   $51.0852   $51.09   $51.10   $51.10  
  Purchase #2 $198.57   8.617%   $215.6808   $215.68   $215.70   $215.70  
  Purchase #3 $105.69   11.635%   $117.987   $117.99   $118.00   $118.00  
  Purchase #4 $179.50   12.359%   $201.6844   $201.68   $201.70   $201.70  
  Purchase #5 $130.55   4.655%   $136.6271   $136.63   $136.65   $136.60  
  Purchase #6 $58.49   10.291%   $64.5092   $64.51   $64.50   $64.50  
  Purchase #7 $109.27   13.332%   $123.8379   $123.84   $123.85   $123.80  
  7 purchase totals = $831.05       $911.4116   $911.42   $911.50   $911.40