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 $208.57   5.556%   $220.1581   $220.16   $220.15   $220.20  
  Purchase #2 $217.30   11.349%   $241.9614   $241.96   $241.95   $242.00  
  Purchase #3 $64.40   5.469%   $67.922   $67.92   $67.90   $67.90  
  Purchase #4 $82.28   7.629%   $88.5571   $88.56   $88.55   $88.60  
  Purchase #5 $167.60   8.718%   $182.2114   $182.21   $182.20   $182.20  
  Purchase #6 $36.53   10.412%   $40.3335   $40.33   $40.35   $40.30  
  Purchase #7 $179.35   7.634%   $193.0416   $193.04   $193.05   $193.00  
  7 purchase totals = $956.03       $1,034.1851   $1,034.18   $1,034.15   $1,034.20