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 $61.85   6.633%   $65.9525   $65.95   $65.95   $66.00  
  Purchase #2 $238.53   10.463%   $263.4874   $263.49   $263.50   $263.50  
  Purchase #3 $195.62   7.310%   $209.9198   $209.92   $209.90   $209.90  
  Purchase #4 $157.37   10.490%   $173.8781   $173.88   $173.90   $173.90  
  Purchase #5 $105.80   10.464%   $116.8709   $116.87   $116.85   $116.90  
  Purchase #6 $174.54   6.358%   $185.6373   $185.64   $185.65   $185.60  
  Purchase #7 $146.73   9.688%   $160.9452   $160.95   $160.95   $160.90  
  7 purchase totals = $1,080.44       $1,176.6912   $1,176.70   $1,176.70   $1,176.70