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 $182.99   10.126%   $201.5196   $201.52   $201.50   $201.50  
  Purchase #2 $80.99   8.298%   $87.7106   $87.71   $87.70   $87.70  
  Purchase #3 $13.76   4.822%   $14.4235   $14.42   $14.40   $14.40  
  Purchase #4 $121.92   8.761%   $132.6014   $132.60   $132.60   $132.60  
  Purchase #5 $36.90   10.330%   $40.7118   $40.71   $40.70   $40.70  
  Purchase #6 $123.39   8.516%   $133.8979   $133.90   $133.90   $133.90  
  Purchase #7 $196.32   5.334%   $206.7917   $206.79   $206.80   $206.80  
  7 purchase totals = $756.27       $817.6565   $817.65   $817.60   $817.60