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 $149.44   12.408%   $167.9825   $167.98   $168.00   $168.00  
  Purchase #2 $22.26   10.476%   $24.592   $24.59   $24.60   $24.60  
  Purchase #3 $95.98   10.410%   $105.9715   $105.97   $105.95   $106.00  
  Purchase #4 $13.46   8.115%   $14.5523   $14.55   $14.55   $14.60  
  Purchase #5 $240.95   8.306%   $260.9633   $260.96   $260.95   $261.00  
  Purchase #6 $23.82   10.145%   $26.2365   $26.24   $26.25   $26.20  
  Purchase #7 $150.33   7.771%   $162.0121   $162.01   $162.00   $162.00  
  7 purchase totals = $696.24       $762.3102   $762.30   $762.30   $762.40