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 $83.73   11.663%   $93.4954   $93.50   $93.50   $93.50  
  Purchase #2 $129.49   8.714%   $140.7738   $140.77   $140.75   $140.80  
  Purchase #3 $29.37   8.867%   $31.9742   $31.97   $31.95   $32.00  
  Purchase #4 $119.77   6.103%   $127.0796   $127.08   $127.10   $127.10  
  Purchase #5 $146.70   11.554%   $163.6497   $163.65   $163.65   $163.60  
  Purchase #6 $238.26   6.417%   $253.5491   $253.55   $253.55   $253.50  
  Purchase #7 $11.61   8.854%   $12.6379   $12.64   $12.65   $12.60  
  7 purchase totals = $758.93       $823.1597   $823.16   $823.15   $823.10