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 $84.88   8.545%   $92.133   $92.13   $92.15   $92.10  
  Purchase #2 $106.89   11.306%   $118.975   $118.98   $119.00   $119.00  
  Purchase #3 $151.64   9.462%   $165.9882   $165.99   $166.00   $166.00  
  Purchase #4 $15.88   9.777%   $17.4326   $17.43   $17.45   $17.40  
  Purchase #5 $153.67   11.676%   $171.6125   $171.61   $171.60   $171.60  
  Purchase #6 $147.58   12.675%   $166.2858   $166.29   $166.30   $166.30  
  Purchase #7 $136.76   11.115%   $151.9609   $151.96   $151.95   $152.00  
  7 purchase totals = $797.30       $884.3880   $884.39   $884.45   $884.40