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 $62.60   6.726%   $66.8105   $66.81   $66.80   $66.80  
  Purchase #2 $191.85   5.314%   $202.0449   $202.04   $202.05   $202.00  
  Purchase #3 $106.51   11.609%   $118.8747   $118.87   $118.85   $118.90  
  Purchase #4 $61.79   11.829%   $69.0991   $69.10   $69.10   $69.10  
  Purchase #5 $127.38   12.487%   $143.2859   $143.29   $143.30   $143.30  
  Purchase #6 $203.79   13.831%   $231.9762   $231.98   $232.00   $232.00  
  Purchase #7 $234.78   5.661%   $248.0709   $248.07   $248.05   $248.10  
  7 purchase totals = $988.70       $1,080.1622   $1,080.16   $1,080.15   $1,080.20