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 $83.68   12.551%   $94.1827   $94.18   $94.20   $94.20  
  Purchase #2 $27.75   4.531%   $29.0074   $29.01   $29.00   $29.00  
  Purchase #3 $30.95   4.185%   $32.2453   $32.25   $32.25   $32.20  
  Purchase #4 $178.55   7.797%   $192.4715   $192.47   $192.45   $192.50  
  Purchase #5 $245.92   7.334%   $263.9558   $263.96   $263.95   $264.00  
  Purchase #6 $7.86   8.491%   $8.5274   $8.53   $8.55   $8.50  
  Purchase #7 $155.46   10.254%   $171.4009   $171.40   $171.40   $171.40  
  7 purchase totals = $730.17       $791.7910   $791.80   $791.80   $791.80