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 $54.70   5.171%   $57.5285   $57.53   $57.55   $57.50  
  Purchase #2 $149.43   9.448%   $163.5481   $163.55   $163.55   $163.50  
  Purchase #3 $186.99   12.151%   $209.7112   $209.71   $209.70   $209.70  
  Purchase #4 $66.54   9.640%   $72.9545   $72.95   $72.95   $73.00  
  Purchase #5 $146.26   3.283%   $151.0617   $151.06   $151.05   $151.10  
  Purchase #6 $221.90   6.291%   $235.8597   $235.86   $235.85   $235.90  
  Purchase #7 $106.29   5.687%   $112.3347   $112.33   $112.35   $112.30  
  7 purchase totals = $932.11       $1,002.9984   $1,002.99   $1,003.00   $1,003.00