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 $84.87   12.824%   $95.7537   $95.75   $95.75   $95.80  
  Purchase #2 $160.65   7.418%   $172.567   $172.57   $172.55   $172.60  
  Purchase #3 $202.50   3.536%   $209.6604   $209.66   $209.65   $209.70  
  Purchase #4 $205.37   8.519%   $222.8655   $222.87   $222.85   $222.90  
  Purchase #5 $100.85   10.770%   $111.7115   $111.71   $111.70   $111.70  
  Purchase #6 $12.84   8.863%   $13.978   $13.98   $14.00   $14.00  
  Purchase #7 $56.68   3.747%   $58.8038   $58.80   $58.80   $58.80  
  7 purchase totals = $823.76       $885.3399   $885.34   $885.30   $885.50