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 $130.27   12.488%   $146.5381   $146.54   $146.55   $146.50  
  Purchase #2 $225.81   11.576%   $251.9498   $251.95   $251.95   $251.90  
  Purchase #3 $63.95   6.774%   $68.282   $68.28   $68.30   $68.30  
  Purchase #4 $228.85   12.614%   $257.7171   $257.72   $257.70   $257.70  
  Purchase #5 $201.82   12.724%   $227.4996   $227.50   $227.50   $227.50  
  Purchase #6 $15.54   5.123%   $16.3361   $16.34   $16.35   $16.30  
  Purchase #7 $93.36   8.140%   $100.9595   $100.96   $100.95   $101.00  
  7 purchase totals = $959.60       $1,069.2822   $1,069.29   $1,069.30   $1,069.20