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 $52.82   12.115%   $59.2191   $59.22   $59.20   $59.20  
  Purchase #2 $217.79   12.772%   $245.6061   $245.61   $245.60   $245.60  
  Purchase #3 $24.41   12.390%   $27.4344   $27.43   $27.45   $27.40  
  Purchase #4 $166.34   11.585%   $185.6105   $185.61   $185.60   $185.60  
  Purchase #5 $182.37   8.287%   $197.483   $197.48   $197.50   $197.50  
  Purchase #6 $192.69   3.688%   $199.7964   $199.80   $199.80   $199.80  
  Purchase #7 $192.72   9.540%   $211.1055   $211.11   $211.10   $211.10  
  7 purchase totals = $1,029.14       $1,126.2550   $1,126.26   $1,126.25   $1,126.20