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 $243.97   9.492%   $267.1276   $267.13   $267.15   $267.10  
  Purchase #2 $198.60   6.672%   $211.8506   $211.85   $211.85   $211.90  
  Purchase #3 $55.81   11.710%   $62.3454   $62.35   $62.35   $62.30  
  Purchase #4 $241.98   5.674%   $255.7099   $255.71   $255.70   $255.70  
  Purchase #5 $22.78   4.299%   $23.7593   $23.76   $23.75   $23.80  
  Purchase #6 $131.53   13.377%   $149.1248   $149.12   $149.10   $149.10  
  Purchase #7 $35.69   4.838%   $37.4167   $37.42   $37.40   $37.40  
  7 purchase totals = $930.36       $1,007.3343   $1,007.34   $1,007.30   $1,007.30