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 $63.26   5.151%   $66.5185   $66.52   $66.50   $66.50  
  Purchase #2 $131.68   4.273%   $137.3067   $137.31   $137.30   $137.30  
  Purchase #3 $65.77   3.355%   $67.9766   $67.98   $68.00   $68.00  
  Purchase #4 $170.97   3.450%   $176.8685   $176.87   $176.85   $176.90  
  Purchase #5 $58.98   13.605%   $67.0042   $67.00   $67.00   $67.00  
  Purchase #6 $56.64   6.501%   $60.3222   $60.32   $60.30   $60.30  
  Purchase #7 $230.28   12.580%   $259.2492   $259.25   $259.25   $259.20  
  7 purchase totals = $777.58       $835.2459   $835.25   $835.20   $835.20