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 $167.88   10.111%   $184.8543   $184.85   $184.85   $184.90  
  Purchase #2 $244.88   5.128%   $257.4374   $257.44   $257.45   $257.40  
  Purchase #3 $104.56   4.564%   $109.3321   $109.33   $109.35   $109.30  
  Purchase #4 $40.99   6.547%   $43.6736   $43.67   $43.65   $43.70  
  Purchase #5 $110.61   4.461%   $115.5443   $115.54   $115.55   $115.50  
  Purchase #6 $250.27   4.132%   $260.6112   $260.61   $260.60   $260.60  
  Purchase #7 $172.64   7.544%   $185.664   $185.66   $185.65   $185.70  
  7 purchase totals = $1,091.83       $1,157.1169   $1,157.10   $1,157.10   $1,157.10