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 $244.70   6.470%   $260.5321   $260.53   $260.55   $260.50  
  Purchase #2 $32.72   9.855%   $35.9446   $35.94   $35.95   $35.90  
  Purchase #3 $77.45   9.115%   $84.5096   $84.51   $84.50   $84.50  
  Purchase #4 $40.54   11.512%   $45.207   $45.21   $45.20   $45.20  
  Purchase #5 $142.45   7.588%   $153.2591   $153.26   $153.25   $153.30  
  Purchase #6 $247.72   3.201%   $255.6495   $255.65   $255.65   $255.60  
  Purchase #7 $162.93   10.354%   $179.7998   $179.80   $179.80   $179.80  
  7 purchase totals = $948.51       $1,014.9017   $1,014.90   $1,014.90   $1,014.80