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 $184.91   13.702%   $210.2464   $210.25   $210.25   $210.20  
  Purchase #2 $145.85   4.856%   $152.9325   $152.93   $152.95   $152.90  
  Purchase #3 $42.78   5.470%   $45.1201   $45.12   $45.10   $45.10  
  Purchase #4 $84.87   10.512%   $93.7915   $93.79   $93.80   $93.80  
  Purchase #5 $189.93   8.261%   $205.6201   $205.62   $205.60   $205.60  
  Purchase #6 $38.63   3.282%   $39.8978   $39.90   $39.90   $39.90  
  Purchase #7 $187.48   3.568%   $194.1693   $194.17   $194.15   $194.20  
  7 purchase totals = $874.45       $941.7777   $941.78   $941.75   $941.70