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 $189.96   7.251%   $203.734   $203.73   $203.75   $203.70  
  Purchase #2 $201.42   6.620%   $214.754   $214.75   $214.75   $214.80  
  Purchase #3 $135.47   8.293%   $146.7045   $146.70   $146.70   $146.70  
  Purchase #4 $134.64   6.195%   $142.9809   $142.98   $143.00   $143.00  
  Purchase #5 $184.55   4.343%   $192.565   $192.57   $192.55   $192.60  
  Purchase #6 $174.76   4.660%   $182.9038   $182.90   $182.90   $182.90  
  Purchase #7 $161.99   12.567%   $182.3473   $182.35   $182.35   $182.30  
  7 purchase totals = $1,182.79       $1,265.9895   $1,265.98   $1,266.00   $1,266.00