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 $67.26   6.330%   $71.5176   $71.52   $71.50   $71.50  
  Purchase #2 $217.99   6.861%   $232.9463   $232.95   $232.95   $232.90  
  Purchase #3 $94.96   3.867%   $98.6321   $98.63   $98.65   $98.60  
  Purchase #4 $38.33   11.818%   $42.8598   $42.86   $42.85   $42.90  
  Purchase #5 $118.50   3.499%   $122.6463   $122.65   $122.65   $122.60  
  Purchase #6 $40.92   5.648%   $43.2312   $43.23   $43.25   $43.20  
  Purchase #7 $151.43   5.462%   $159.7011   $159.70   $159.70   $159.70  
  7 purchase totals = $729.39       $771.5344   $771.54   $771.55   $771.40