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 $24.74   7.541%   $26.6056   $26.61   $26.60   $26.60  
  Purchase #2 $70.26   4.816%   $73.6437   $73.64   $73.65   $73.60  
  Purchase #3 $161.98   5.498%   $170.8857   $170.89   $170.90   $170.90  
  Purchase #4 $193.75   4.378%   $202.2324   $202.23   $202.25   $202.20  
  Purchase #5 $156.70   10.635%   $173.365   $173.37   $173.35   $173.40  
  Purchase #6 $143.72   6.461%   $153.0057   $153.01   $153.00   $153.00  
  Purchase #7 $212.79   7.712%   $229.2004   $229.20   $229.20   $229.20  
  7 purchase totals = $963.94       $1,028.9385   $1,028.95   $1,028.95   $1,028.90