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 $54.36   4.280%   $56.6866   $56.69   $56.70   $56.70  
  Purchase #2 $9.51   7.262%   $10.2006   $10.20   $10.20   $10.20  
  Purchase #3 $151.84   7.167%   $162.7224   $162.72   $162.70   $162.70  
  Purchase #4 $232.47   12.353%   $261.187   $261.19   $261.20   $261.20  
  Purchase #5 $24.83   6.363%   $26.4099   $26.41   $26.40   $26.40  
  Purchase #6 $233.49   4.546%   $244.1045   $244.10   $244.10   $244.10  
  Purchase #7 $28.43   12.852%   $32.0838   $32.08   $32.10   $32.10  
  7 purchase totals = $734.93       $793.3948   $793.39   $793.40   $793.40