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 $227.48   8.190%   $246.1106   $246.11   $246.10   $246.10  
  Purchase #2 $168.39   5.133%   $177.0335   $177.03   $177.05   $177.00  
  Purchase #3 $51.98   11.479%   $57.9468   $57.95   $57.95   $57.90  
  Purchase #4 $229.77   5.259%   $241.8536   $241.85   $241.85   $241.90  
  Purchase #5 $238.47   9.672%   $261.5348   $261.53   $261.55   $261.50  
  Purchase #6 $247.36   6.270%   $262.8695   $262.87   $262.85   $262.90  
  Purchase #7 $227.38   4.699%   $238.0646   $238.06   $238.05   $238.10  
  7 purchase totals = $1,390.83       $1,485.4134   $1,485.40   $1,485.40   $1,485.40