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 $250.94   9.197%   $274.019   $274.02   $274.00   $274.00  
  Purchase #2 $200.99   4.144%   $209.319   $209.32   $209.30   $209.30  
  Purchase #3 $53.27   4.371%   $55.5984   $55.60   $55.60   $55.60  
  Purchase #4 $39.38   7.264%   $42.2406   $42.24   $42.25   $42.20  
  Purchase #5 $173.25   12.760%   $195.3567   $195.36   $195.35   $195.40  
  Purchase #6 $212.81   10.310%   $234.7507   $234.75   $234.75   $234.80  
  Purchase #7 $84.28   12.288%   $94.6363   $94.64   $94.65   $94.60  
  7 purchase totals = $1,014.92       $1,105.9207   $1,105.93   $1,105.90   $1,105.90