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 $123.87   13.556%   $140.6618   $140.66   $140.65   $140.70  
  Purchase #2 $245.32   9.335%   $268.2206   $268.22   $268.20   $268.20  
  Purchase #3 $70.80   12.207%   $79.4426   $79.44   $79.45   $79.40  
  Purchase #4 $149.75   12.372%   $168.2771   $168.28   $168.30   $168.30  
  Purchase #5 $64.42   13.188%   $72.9157   $72.92   $72.90   $72.90  
  Purchase #6 $224.68   6.833%   $240.0324   $240.03   $240.05   $240.00  
  Purchase #7 $223.47   6.867%   $238.8157   $238.82   $238.80   $238.80  
  7 purchase totals = $1,102.31       $1,208.3659   $1,208.37   $1,208.35   $1,208.30