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 $113.98   11.460%   $127.0421   $127.04   $127.05   $127.00  
  Purchase #2 $124.69   10.376%   $137.6278   $137.63   $137.65   $137.60  
  Purchase #3 $243.41   5.531%   $256.873   $256.87   $256.85   $256.90  
  Purchase #4 $25.69   13.307%   $29.1086   $29.11   $29.10   $29.10  
  Purchase #5 $15.25   7.150%   $16.3404   $16.34   $16.35   $16.30  
  Purchase #6 $178.39   13.801%   $203.0096   $203.01   $203.00   $203.00  
  Purchase #7 $113.94   11.268%   $126.7788   $126.78   $126.80   $126.80  
  7 purchase totals = $815.35       $896.7803   $896.78   $896.80   $896.70