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 $58.31   7.658%   $62.7754   $62.78   $62.80   $62.80  
  Purchase #2 $166.50   6.366%   $177.0994   $177.10   $177.10   $177.10  
  Purchase #3 $7.30   7.376%   $7.8384   $7.84   $7.85   $7.80  
  Purchase #4 $163.42   5.304%   $172.0878   $172.09   $172.10   $172.10  
  Purchase #5 $211.43   8.180%   $228.725   $228.73   $228.75   $228.70  
  Purchase #6 $17.59   8.233%   $19.0382   $19.04   $19.05   $19.00  
  Purchase #7 $113.27   11.679%   $126.4988   $126.50   $126.50   $126.50  
  7 purchase totals = $737.82       $794.0630   $794.08   $794.15   $794.00