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 $87.88   8.311%   $95.1837   $95.18   $95.20   $95.20  
  Purchase #2 $43.69   13.599%   $49.6314   $49.63   $49.65   $49.60  
  Purchase #3 $238.92   11.529%   $266.4651   $266.47   $266.45   $266.50  
  Purchase #4 $123.62   4.170%   $128.775   $128.78   $128.80   $128.80  
  Purchase #5 $40.45   9.150%   $44.1512   $44.15   $44.15   $44.20  
  Purchase #6 $139.93   5.304%   $147.3519   $147.35   $147.35   $147.40  
  Purchase #7 $16.25   7.494%   $17.4678   $17.47   $17.45   $17.50  
  7 purchase totals = $690.74       $749.0261   $749.03   $749.05   $749.20