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 $119.64   6.121%   $126.9632   $126.96   $126.95   $127.00  
  Purchase #2 $25.73   6.622%   $27.4338   $27.43   $27.45   $27.40  
  Purchase #3 $60.67   7.473%   $65.2039   $65.20   $65.20   $65.20  
  Purchase #4 $232.40   10.744%   $257.3691   $257.37   $257.35   $257.40  
  Purchase #5 $128.81   13.421%   $146.0976   $146.10   $146.10   $146.10  
  Purchase #6 $74.93   9.102%   $81.7501   $81.75   $81.75   $81.80  
  Purchase #7 $83.87   5.642%   $88.6019   $88.60   $88.60   $88.60  
  7 purchase totals = $726.05       $793.4196   $793.41   $793.40   $793.50