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 $161.98   13.507%   $183.8586   $183.86   $183.85   $183.90  
  Purchase #2 $200.47   5.806%   $212.1093   $212.11   $212.10   $212.10  
  Purchase #3 $141.47   9.361%   $154.713   $154.71   $154.70   $154.70  
  Purchase #4 $24.32   3.261%   $25.1131   $25.11   $25.10   $25.10  
  Purchase #5 $217.48   3.321%   $224.7025   $224.70   $224.70   $224.70  
  Purchase #6 $234.47   9.158%   $255.9428   $255.94   $255.95   $255.90  
  Purchase #7 $134.49   7.263%   $144.258   $144.26   $144.25   $144.30  
  7 purchase totals = $1,114.68       $1,200.6973   $1,200.69   $1,200.65   $1,200.70