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 $49.90   5.553%   $52.6709   $52.67   $52.65   $52.70  
  Purchase #2 $247.88   11.684%   $276.8423   $276.84   $276.85   $276.80  
  Purchase #3 $43.31   11.586%   $48.3279   $48.33   $48.35   $48.30  
  Purchase #4 $156.84   8.348%   $169.933   $169.93   $169.95   $169.90  
  Purchase #5 $128.81   12.300%   $144.6536   $144.65   $144.65   $144.70  
  Purchase #6 $54.32   8.521%   $58.9486   $58.95   $58.95   $58.90  
  Purchase #7 $229.78   6.398%   $244.4813   $244.48   $244.50   $244.50  
  7 purchase totals = $910.84       $995.8576   $995.85   $995.90   $995.80