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 $74.35   11.588%   $82.9657   $82.97   $82.95   $83.00  
  Purchase #2 $97.38   13.231%   $110.2643   $110.26   $110.25   $110.30  
  Purchase #3 $104.68   8.537%   $113.6165   $113.62   $113.60   $113.60  
  Purchase #4 $50.32   4.662%   $52.6659   $52.67   $52.65   $52.70  
  Purchase #5 $236.63   4.234%   $246.6489   $246.65   $246.65   $246.60  
  Purchase #6 $121.45   10.712%   $134.4597   $134.46   $134.45   $134.50  
  Purchase #7 $208.97   12.861%   $235.8456   $235.85   $235.85   $235.80  
  7 purchase totals = $893.78       $976.4666   $976.48   $976.40   $976.50