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 $84.66   11.383%   $94.2968   $94.30   $94.30   $94.30  
  Purchase #2 $92.98   7.551%   $100.0009   $100.00   $100.00   $100.00  
  Purchase #3 $191.49   11.634%   $213.7679   $213.77   $213.75   $213.80  
  Purchase #4 $21.84   10.557%   $24.1456   $24.15   $24.15   $24.10  
  Purchase #5 $216.45   3.443%   $223.9024   $223.90   $223.90   $223.90  
  Purchase #6 $162.77   9.378%   $178.0346   $178.03   $178.05   $178.00  
  Purchase #7 $233.78   5.587%   $246.8413   $246.84   $246.85   $246.80  
  7 purchase totals = $1,003.97       $1,080.9895   $1,080.99   $1,081.00   $1,080.90