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 $85.73   12.452%   $96.4051   $96.41   $96.40   $96.40  
  Purchase #2 $50.91   12.802%   $57.4275   $57.43   $57.45   $57.40  
  Purchase #3 $207.91   8.815%   $226.2373   $226.24   $226.25   $226.20  
  Purchase #4 $59.94   7.209%   $64.2611   $64.26   $64.25   $64.30  
  Purchase #5 $115.34   3.248%   $119.0862   $119.09   $119.10   $119.10  
  Purchase #6 $215.43   9.453%   $235.7946   $235.79   $235.80   $235.80  
  Purchase #7 $237.61   12.570%   $267.4776   $267.48   $267.50   $267.50  
  7 purchase totals = $972.87       $1,066.6894   $1,066.70   $1,066.75   $1,066.70