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 $54.80   11.778%   $61.2543   $61.25   $61.25   $61.30  
  Purchase #2 $192.95   4.626%   $201.8759   $201.88   $201.90   $201.90  
  Purchase #3 $109.96   7.674%   $118.3983   $118.40   $118.40   $118.40  
  Purchase #4 $152.44   3.351%   $157.5483   $157.55   $157.55   $157.50  
  Purchase #5 $90.71   7.521%   $97.5323   $97.53   $97.55   $97.50  
  Purchase #6 $131.52   4.862%   $137.9145   $137.91   $137.90   $137.90  
  Purchase #7 $125.63   12.490%   $141.3212   $141.32   $141.30   $141.30  
  7 purchase totals = $858.01       $915.8448   $915.84   $915.85   $915.80