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 $144.77   8.581%   $157.1927   $157.19   $157.20   $157.20  
  Purchase #2 $230.61   11.454%   $257.0241   $257.02   $257.00   $257.00  
  Purchase #3 $56.26   5.109%   $59.1343   $59.13   $59.15   $59.10  
  Purchase #4 $202.37   5.745%   $213.9962   $214.00   $214.00   $214.00  
  Purchase #5 $106.62   12.394%   $119.8345   $119.83   $119.85   $119.80  
  Purchase #6 $154.34   5.397%   $162.6697   $162.67   $162.65   $162.70  
  Purchase #7 $44.40   13.660%   $50.465   $50.47   $50.45   $50.50  
  7 purchase totals = $939.37       $1,020.3165   $1,020.31   $1,020.30   $1,020.30