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 $58.39   10.477%   $64.5075   $64.51   $64.50   $64.50  
  Purchase #2 $160.29   13.295%   $181.6006   $181.60   $181.60   $181.60  
  Purchase #3 $38.48   7.337%   $41.3033   $41.30   $41.30   $41.30  
  Purchase #4 $77.87   7.519%   $83.725   $83.73   $83.75   $83.70  
  Purchase #5 $150.55   4.703%   $157.6304   $157.63   $157.65   $157.60  
  Purchase #6 $108.57   4.456%   $113.4079   $113.41   $113.40   $113.40  
  Purchase #7 $120.60   5.600%   $127.3536   $127.35   $127.35   $127.40  
  7 purchase totals = $714.75       $769.5283   $769.53   $769.55   $769.50