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 $24.82   7.369%   $26.649   $26.65   $26.65   $26.60  
  Purchase #2 $66.34   11.158%   $73.7422   $73.74   $73.75   $73.70  
  Purchase #3 $25.32   3.581%   $26.2267   $26.23   $26.25   $26.20  
  Purchase #4 $62.46   4.836%   $65.4806   $65.48   $65.50   $65.50  
  Purchase #5 $197.82   5.874%   $209.4399   $209.44   $209.45   $209.40  
  Purchase #6 $156.61   10.287%   $172.7205   $172.72   $172.70   $172.70  
  Purchase #7 $207.52   6.480%   $220.9673   $220.97   $220.95   $221.00  
  7 purchase totals = $740.89       $795.2262   $795.23   $795.25   $795.10