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 $41.29   6.210%   $43.8541   $43.85   $43.85   $43.90  
  Purchase #2 $140.96   10.401%   $155.6212   $155.62   $155.60   $155.60  
  Purchase #3 $218.66   7.443%   $234.9349   $234.93   $234.95   $234.90  
  Purchase #4 $55.77   12.354%   $62.6598   $62.66   $62.65   $62.70  
  Purchase #5 $76.90   3.355%   $79.48   $79.48   $79.50   $79.50  
  Purchase #6 $59.72   3.617%   $61.8801   $61.88   $61.90   $61.90  
  Purchase #7 $15.35   6.359%   $16.3261   $16.33   $16.35   $16.30  
  7 purchase totals = $608.65       $654.7562   $654.75   $654.80   $654.80