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 $10.67   11.681%   $11.9164   $11.92   $11.90   $11.90  
  Purchase #2 $55.85   4.639%   $58.4409   $58.44   $58.45   $58.40  
  Purchase #3 $161.72   4.781%   $169.4518   $169.45   $169.45   $169.50  
  Purchase #4 $235.37   13.387%   $266.879   $266.88   $266.90   $266.90  
  Purchase #5 $81.60   8.703%   $88.7016   $88.70   $88.70   $88.70  
  Purchase #6 $204.57   5.629%   $216.0852   $216.09   $216.10   $216.10  
  Purchase #7 $76.28   10.380%   $84.1979   $84.20   $84.20   $84.20  
  7 purchase totals = $826.06       $895.6728   $895.68   $895.70   $895.70