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 $20.25   10.806%   $22.4382   $22.44   $22.45   $22.40  
  Purchase #2 $138.44   7.703%   $149.104   $149.10   $149.10   $149.10  
  Purchase #3 $103.83   12.139%   $116.4339   $116.43   $116.45   $116.40  
  Purchase #4 $35.42   10.114%   $39.0024   $39.00   $39.00   $39.00  
  Purchase #5 $134.81   4.434%   $140.7875   $140.79   $140.80   $140.80  
  Purchase #6 $167.91   12.496%   $188.892   $188.89   $188.90   $188.90  
  Purchase #7 $217.47   10.605%   $240.5327   $240.53   $240.55   $240.50  
  7 purchase totals = $818.13       $897.1907   $897.18   $897.25   $897.10