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 $87.47   10.592%   $96.7348   $96.73   $96.75   $96.70  
  Purchase #2 $74.40   11.260%   $82.7774   $82.78   $82.80   $82.80  
  Purchase #3 $173.25   4.172%   $180.478   $180.48   $180.50   $180.50  
  Purchase #4 $247.81   8.684%   $269.3298   $269.33   $269.35   $269.30  
  Purchase #5 $78.62   5.321%   $82.8034   $82.80   $82.80   $82.80  
  Purchase #6 $131.99   6.716%   $140.8544   $140.85   $140.85   $140.90  
  Purchase #7 $87.85   10.366%   $96.9565   $96.96   $96.95   $97.00  
  7 purchase totals = $881.39       $949.9343   $949.93   $950.00   $950.00