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 $59.28   6.686%   $63.2435   $63.24   $63.25   $63.20  
  Purchase #2 $87.66   4.710%   $91.7888   $91.79   $91.80   $91.80  
  Purchase #3 $73.73   5.321%   $77.6532   $77.65   $77.65   $77.70  
  Purchase #4 $109.66   12.325%   $123.1756   $123.18   $123.20   $123.20  
  Purchase #5 $190.67   5.399%   $200.9643   $200.96   $200.95   $201.00  
  Purchase #6 $121.90   11.516%   $135.938   $135.94   $135.95   $135.90  
  Purchase #7 $21.52   12.232%   $24.1523   $24.15   $24.15   $24.20  
  7 purchase totals = $664.42       $716.9157   $716.91   $716.95   $717.00