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 $219.52   3.641%   $227.5127   $227.51   $227.50   $227.50  
  Purchase #2 $169.61   8.634%   $184.2541   $184.25   $184.25   $184.30  
  Purchase #3 $119.60   3.414%   $123.6831   $123.68   $123.70   $123.70  
  Purchase #4 $104.73   5.563%   $110.5561   $110.56   $110.55   $110.60  
  Purchase #5 $206.84   12.620%   $232.9432   $232.94   $232.95   $232.90  
  Purchase #6 $71.83   4.310%   $74.9259   $74.93   $74.95   $74.90  
  Purchase #7 $179.76   10.369%   $198.3993   $198.40   $198.40   $198.40  
  7 purchase totals = $1,071.89       $1,152.2744   $1,152.27   $1,152.30   $1,152.30