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 $53.54   8.251%   $57.9576   $57.96   $57.95   $58.00  
  Purchase #2 $105.81   11.385%   $117.8565   $117.86   $117.85   $117.90  
  Purchase #3 $77.93   8.570%   $84.6086   $84.61   $84.60   $84.60  
  Purchase #4 $231.84   4.377%   $241.9876   $241.99   $242.00   $242.00  
  Purchase #5 $71.30   6.154%   $75.6878   $75.69   $75.70   $75.70  
  Purchase #6 $74.64   5.430%   $78.693   $78.69   $78.70   $78.70  
  Purchase #7 $105.37   7.405%   $113.1726   $113.17   $113.15   $113.20  
  7 purchase totals = $720.43       $769.9637   $769.97   $769.95   $770.10