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 $121.41   3.565%   $125.7383   $125.74   $125.75   $125.70  
  Purchase #2 $221.57   10.331%   $244.4604   $244.46   $244.45   $244.50  
  Purchase #3 $30.62   4.753%   $32.0754   $32.08   $32.10   $32.10  
  Purchase #4 $133.27   3.838%   $138.3849   $138.38   $138.40   $138.40  
  Purchase #5 $85.72   12.309%   $96.2713   $96.27   $96.25   $96.30  
  Purchase #6 $236.54   13.442%   $268.3357   $268.34   $268.35   $268.30  
  Purchase #7 $52.59   5.695%   $55.585   $55.59   $55.60   $55.60  
  7 purchase totals = $881.72       $960.8510   $960.86   $960.90   $960.90