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 $53.78   4.747%   $56.3329   $56.33   $56.35   $56.30  
  Purchase #2 $207.37   7.423%   $222.7631   $222.76   $222.75   $222.80  
  Purchase #3 $230.98   13.286%   $261.668   $261.67   $261.65   $261.70  
  Purchase #4 $241.56   5.231%   $254.196   $254.20   $254.20   $254.20  
  Purchase #5 $218.42   11.565%   $243.6803   $243.68   $243.70   $243.70  
  Purchase #6 $24.71   9.248%   $26.9952   $27.00   $27.00   $27.00  
  Purchase #7 $187.58   3.431%   $194.0159   $194.02   $194.00   $194.00  
  7 purchase totals = $1,164.40       $1,259.6514   $1,259.66   $1,259.65   $1,259.70