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 $63.36   7.267%   $67.9644   $67.96   $67.95   $68.00  
  Purchase #2 $29.77   7.779%   $32.0858   $32.09   $32.10   $32.10  
  Purchase #3 $57.69   11.585%   $64.3734   $64.37   $64.35   $64.40  
  Purchase #4 $149.69   12.476%   $168.3653   $168.37   $168.35   $168.40  
  Purchase #5 $226.51   11.763%   $253.1544   $253.15   $253.15   $253.20  
  Purchase #6 $100.50   4.326%   $104.8476   $104.85   $104.85   $104.80  
  Purchase #7 $29.54   8.590%   $32.0775   $32.08   $32.10   $32.10  
  7 purchase totals = $657.06       $722.8684   $722.87   $722.85   $723.00