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 $202.42   12.689%   $228.1051   $228.11   $228.10   $228.10  
  Purchase #2 $92.37   4.711%   $96.7216   $96.72   $96.70   $96.70  
  Purchase #3 $48.69   3.662%   $50.473   $50.47   $50.45   $50.50  
  Purchase #4 $230.69   5.282%   $242.875   $242.88   $242.90   $242.90  
  Purchase #5 $109.87   6.407%   $116.9094   $116.91   $116.90   $116.90  
  Purchase #6 $26.77   10.171%   $29.4928   $29.49   $29.50   $29.50  
  Purchase #7 $170.46   5.228%   $179.3716   $179.37   $179.35   $179.40  
  7 purchase totals = $881.27       $943.9485   $943.95   $943.90   $944.00