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 $241.69   6.335%   $257.0011   $257.00   $257.00   $257.00  
  Purchase #2 $130.78   7.829%   $141.0188   $141.02   $141.00   $141.00  
  Purchase #3 $10.37   13.463%   $11.7661   $11.77   $11.75   $11.80  
  Purchase #4 $41.73   4.453%   $43.5882   $43.59   $43.60   $43.60  
  Purchase #5 $158.34   9.722%   $173.7338   $173.73   $173.75   $173.70  
  Purchase #6 $212.65   13.424%   $241.1961   $241.20   $241.20   $241.20  
  Purchase #7 $101.53   5.538%   $107.1527   $107.15   $107.15   $107.20  
  7 purchase totals = $897.09       $975.4568   $975.46   $975.45   $975.50