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 $144.88   11.484%   $161.518   $161.52   $161.50   $161.50  
  Purchase #2 $158.38   7.194%   $169.7739   $169.77   $169.75   $169.80  
  Purchase #3 $23.66   12.362%   $26.5848   $26.58   $26.60   $26.60  
  Purchase #4 $153.39   13.718%   $174.432   $174.43   $174.45   $174.40  
  Purchase #5 $107.34   7.287%   $115.1619   $115.16   $115.15   $115.20  
  Purchase #6 $203.56   11.480%   $226.9287   $226.93   $226.95   $226.90  
  Purchase #7 $74.93   7.782%   $80.7611   $80.76   $80.75   $80.80  
  7 purchase totals = $866.14       $955.1604   $955.15   $955.15   $955.20