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 $192.72   7.853%   $207.8543   $207.85   $207.85   $207.90  
  Purchase #2 $70.88   4.299%   $73.9271   $73.93   $73.95   $73.90  
  Purchase #3 $29.35   7.227%   $31.4711   $31.47   $31.45   $31.50  
  Purchase #4 $186.66   4.263%   $194.6173   $194.62   $194.60   $194.60  
  Purchase #5 $120.62   6.763%   $128.7775   $128.78   $128.80   $128.80  
  Purchase #6 $118.66   3.302%   $122.5782   $122.58   $122.60   $122.60  
  Purchase #7 $193.28   7.202%   $207.2   $207.20   $207.20   $207.20  
  7 purchase totals = $912.17       $966.4255   $966.43   $966.45   $966.50