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 $203.45   5.188%   $214.005   $214.01   $214.00   $214.00  
  Purchase #2 $77.57   10.228%   $85.5039   $85.50   $85.50   $85.50  
  Purchase #3 $77.30   5.176%   $81.301   $81.30   $81.30   $81.30  
  Purchase #4 $200.75   5.846%   $212.4858   $212.49   $212.50   $212.50  
  Purchase #5 $103.83   11.717%   $115.9958   $116.00   $116.00   $116.00  
  Purchase #6 $152.99   4.568%   $159.9786   $159.98   $160.00   $160.00  
  Purchase #7 $70.48   3.870%   $73.2076   $73.21   $73.20   $73.20  
  7 purchase totals = $886.37       $942.4777   $942.49   $942.50   $942.50