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 $205.38   10.266%   $226.4643   $226.46   $226.45   $226.50  
  Purchase #2 $149.40   13.688%   $169.8499   $169.85   $169.85   $169.80  
  Purchase #3 $157.80   10.496%   $174.3627   $174.36   $174.35   $174.40  
  Purchase #4 $240.93   12.833%   $271.8485   $271.85   $271.85   $271.80  
  Purchase #5 $97.55   13.824%   $111.0353   $111.04   $111.05   $111.00  
  Purchase #6 $25.90   6.819%   $27.6661   $27.67   $27.65   $27.70  
  Purchase #7 $95.66   9.146%   $104.4091   $104.41   $104.40   $104.40  
  7 purchase totals = $972.62       $1,085.6359   $1,085.64   $1,085.60   $1,085.60