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 $207.47   10.489%   $229.2315   $229.23   $229.25   $229.20  
  Purchase #2 $244.74   12.611%   $275.6042   $275.60   $275.60   $275.60  
  Purchase #3 $244.64   11.710%   $273.2873   $273.29   $273.30   $273.30  
  Purchase #4 $151.95   9.651%   $166.6147   $166.61   $166.60   $166.60  
  Purchase #5 $68.39   11.628%   $76.3424   $76.34   $76.35   $76.30  
  Purchase #6 $73.80   7.410%   $79.2686   $79.27   $79.25   $79.30  
  Purchase #7 $245.45   9.707%   $269.2758   $269.28   $269.30   $269.30  
  7 purchase totals = $1,236.44       $1,369.6245   $1,369.62   $1,369.65   $1,369.60