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 $60.52   11.872%   $67.7049   $67.70   $67.70   $67.70  
  Purchase #2 $153.27   10.330%   $169.1028   $169.10   $169.10   $169.10  
  Purchase #3 $250.33   6.214%   $265.8855   $265.89   $265.90   $265.90  
  Purchase #4 $99.44   12.820%   $112.1882   $112.19   $112.20   $112.20  
  Purchase #5 $212.72   4.533%   $222.3626   $222.36   $222.35   $222.40  
  Purchase #6 $195.71   11.115%   $217.4632   $217.46   $217.45   $217.50  
  Purchase #7 $242.92   4.129%   $252.9502   $252.95   $252.95   $253.00  
  7 purchase totals = $1,214.91       $1,307.6574   $1,307.65   $1,307.65   $1,307.80