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 $90.98   3.385%   $94.0597   $94.06   $94.05   $94.10  
  Purchase #2 $175.75   9.116%   $191.7714   $191.77   $191.75   $191.80  
  Purchase #3 $60.82   13.261%   $68.8853   $68.89   $68.90   $68.90  
  Purchase #4 $238.54   4.799%   $249.9875   $249.99   $250.00   $250.00  
  Purchase #5 $189.60   5.133%   $199.3322   $199.33   $199.35   $199.30  
  Purchase #6 $126.93   11.159%   $141.0941   $141.09   $141.10   $141.10  
  Purchase #7 $116.40   8.296%   $126.0565   $126.06   $126.05   $126.10  
  7 purchase totals = $999.02       $1,071.1867   $1,071.19   $1,071.20   $1,071.30