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 $62.62   8.642%   $68.0316   $68.03   $68.05   $68.00  
  Purchase #2 $110.68   11.274%   $123.1581   $123.16   $123.15   $123.20  
  Purchase #3 $146.97   4.507%   $153.5939   $153.59   $153.60   $153.60  
  Purchase #4 $92.97   9.489%   $101.7919   $101.79   $101.80   $101.80  
  Purchase #5 $120.57   4.828%   $126.3911   $126.39   $126.40   $126.40  
  Purchase #6 $69.94   11.842%   $78.2223   $78.22   $78.20   $78.20  
  Purchase #7 $157.56   5.409%   $166.0824   $166.08   $166.10   $166.10  
  7 purchase totals = $761.31       $817.2713   $817.26   $817.30   $817.30