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 $71.75   11.450%   $79.9654   $79.97   $79.95   $80.00  
  Purchase #2 $157.66   10.307%   $173.91   $173.91   $173.90   $173.90  
  Purchase #3 $39.51   12.667%   $44.5147   $44.51   $44.50   $44.50  
  Purchase #4 $86.48   6.811%   $92.3702   $92.37   $92.35   $92.40  
  Purchase #5 $195.75   7.115%   $209.6776   $209.68   $209.70   $209.70  
  Purchase #6 $159.52   4.397%   $166.5341   $166.53   $166.55   $166.50  
  Purchase #7 $62.46   5.615%   $65.9671   $65.97   $65.95   $66.00  
  7 purchase totals = $773.13       $832.9391   $832.94   $832.90   $833.00