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 $81.91   12.807%   $92.4002   $92.40   $92.40   $92.40  
  Purchase #2 $119.69   13.544%   $135.9008   $135.90   $135.90   $135.90  
  Purchase #3 $92.60   11.102%   $102.8805   $102.88   $102.90   $102.90  
  Purchase #4 $153.64   11.259%   $170.9383   $170.94   $170.95   $170.90  
  Purchase #5 $169.40   4.194%   $176.5046   $176.50   $176.50   $176.50  
  Purchase #6 $76.76   13.762%   $87.3237   $87.32   $87.30   $87.30  
  Purchase #7 $176.52   4.644%   $184.7176   $184.72   $184.70   $184.70  
  7 purchase totals = $870.52       $950.6657   $950.66   $950.65   $950.60