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 $61.87   10.169%   $68.1616   $68.16   $68.15   $68.20  
  Purchase #2 $152.86   12.863%   $172.5224   $172.52   $172.50   $172.50  
  Purchase #3 $193.88   5.160%   $203.8842   $203.88   $203.90   $203.90  
  Purchase #4 $209.84   5.814%   $222.0401   $222.04   $222.05   $222.00  
  Purchase #5 $95.80   3.435%   $99.0907   $99.09   $99.10   $99.10  
  Purchase #6 $68.65   9.384%   $75.0921   $75.09   $75.10   $75.10  
  Purchase #7 $190.26   13.141%   $215.2621   $215.26   $215.25   $215.30  
  7 purchase totals = $973.16       $1,056.0532   $1,056.04   $1,056.05   $1,056.10