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 $60.28   11.428%   $67.1688   $67.17   $67.15   $67.20  
  Purchase #2 $141.37   9.145%   $154.2983   $154.30   $154.30   $154.30  
  Purchase #3 $132.32   9.851%   $145.3548   $145.35   $145.35   $145.40  
  Purchase #4 $167.60   11.453%   $186.7952   $186.80   $186.80   $186.80  
  Purchase #5 $189.87   13.337%   $215.193   $215.19   $215.20   $215.20  
  Purchase #6 $44.27   3.603%   $45.865   $45.87   $45.85   $45.90  
  Purchase #7 $162.41   13.340%   $184.0755   $184.08   $184.10   $184.10  
  7 purchase totals = $898.12       $998.7506   $998.76   $998.75   $998.90