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 $25.48   3.150%   $26.2826   $26.28   $26.30   $26.30  
  Purchase #2 $199.55   9.165%   $217.8388   $217.84   $217.85   $217.80  
  Purchase #3 $131.27   8.117%   $141.9252   $141.93   $141.95   $141.90  
  Purchase #4 $240.78   11.215%   $267.7835   $267.78   $267.80   $267.80  
  Purchase #5 $212.51   13.185%   $240.5294   $240.53   $240.55   $240.50  
  Purchase #6 $99.81   12.409%   $112.1954   $112.20   $112.20   $112.20  
  Purchase #7 $36.28   11.151%   $40.3256   $40.33   $40.35   $40.30  
  7 purchase totals = $945.68       $1,046.8805   $1,046.89   $1,047.00   $1,046.80