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 $182.94   6.459%   $194.7561   $194.76   $194.75   $194.80  
  Purchase #2 $10.68   9.314%   $11.6747   $11.67   $11.65   $11.70  
  Purchase #3 $102.88   13.380%   $116.6453   $116.65   $116.65   $116.60  
  Purchase #4 $216.52   4.356%   $225.9516   $225.95   $225.95   $226.00  
  Purchase #5 $114.33   4.857%   $119.883   $119.88   $119.90   $119.90  
  Purchase #6 $9.74   13.295%   $11.0349   $11.03   $11.05   $11.00  
  Purchase #7 $96.72   13.287%   $109.5712   $109.57   $109.55   $109.60  
  7 purchase totals = $733.81       $789.5168   $789.51   $789.50   $789.60