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 $150.57   7.339%   $161.6203   $161.62   $161.60   $161.60  
  Purchase #2 $241.45   9.303%   $263.9121   $263.91   $263.90   $263.90  
  Purchase #3 $157.68   6.782%   $168.3739   $168.37   $168.35   $168.40  
  Purchase #4 $69.91   4.869%   $73.3139   $73.31   $73.30   $73.30  
  Purchase #5 $94.84   13.168%   $107.3285   $107.33   $107.35   $107.30  
  Purchase #6 $104.76   11.591%   $116.9027   $116.90   $116.90   $116.90  
  Purchase #7 $159.39   5.226%   $167.7197   $167.72   $167.70   $167.70  
  7 purchase totals = $978.60       $1,059.1711   $1,059.16   $1,059.10   $1,059.10