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 $88.85   4.138%   $92.5266   $92.53   $92.55   $92.50  
  Purchase #2 $157.68   3.836%   $163.7286   $163.73   $163.75   $163.70  
  Purchase #3 $90.94   9.593%   $99.6639   $99.66   $99.65   $99.70  
  Purchase #4 $56.62   7.545%   $60.892   $60.89   $60.90   $60.90  
  Purchase #5 $50.42   4.856%   $52.8684   $52.87   $52.85   $52.90  
  Purchase #6 $129.34   8.120%   $139.8424   $139.84   $139.85   $139.80  
  Purchase #7 $196.26   8.255%   $212.4613   $212.46   $212.45   $212.50  
  7 purchase totals = $770.11       $821.9832   $821.98   $822.00   $822.00