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 $101.35   11.246%   $112.7478   $112.75   $112.75   $112.70  
  Purchase #2 $160.37   3.704%   $166.3101   $166.31   $166.30   $166.30  
  Purchase #3 $53.61   13.295%   $60.7374   $60.74   $60.75   $60.70  
  Purchase #4 $168.52   4.546%   $176.1809   $176.18   $176.20   $176.20  
  Purchase #5 $163.93   12.286%   $184.0704   $184.07   $184.05   $184.10  
  Purchase #6 $221.28   6.267%   $235.1476   $235.15   $235.15   $235.10  
  Purchase #7 $32.31   5.313%   $34.0266   $34.03   $34.05   $34.00  
  7 purchase totals = $901.37       $969.2208   $969.23   $969.25   $969.10