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 $48.71   11.763%   $54.4398   $54.44   $54.45   $54.40  
  Purchase #2 $83.35   9.529%   $91.2924   $91.29   $91.30   $91.30  
  Purchase #3 $191.87   10.764%   $212.5229   $212.52   $212.50   $212.50  
  Purchase #4 $17.37   3.603%   $17.9958   $18.00   $18.00   $18.00  
  Purchase #5 $82.44   3.335%   $85.1894   $85.19   $85.20   $85.20  
  Purchase #6 $168.47   4.552%   $176.1388   $176.14   $176.15   $176.10  
  Purchase #7 $179.41   5.220%   $188.7752   $188.78   $188.80   $188.80  
  7 purchase totals = $771.62       $826.3543   $826.36   $826.40   $826.30