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 $134.66   13.637%   $153.0236   $153.02   $153.00   $153.00  
  Purchase #2 $39.98   4.347%   $41.7179   $41.72   $41.70   $41.70  
  Purchase #3 $236.32   7.546%   $254.1527   $254.15   $254.15   $254.20  
  Purchase #4 $14.82   4.283%   $15.4547   $15.45   $15.45   $15.50  
  Purchase #5 $57.46   4.414%   $59.9963   $60.00   $60.00   $60.00  
  Purchase #6 $166.99   5.147%   $175.585   $175.59   $175.60   $175.60  
  Purchase #7 $88.27   11.482%   $98.4052   $98.41   $98.40   $98.40  
  7 purchase totals = $738.50       $798.3354   $798.34   $798.30   $798.40