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 $64.83   7.488%   $69.6845   $69.68   $69.70   $69.70  
  Purchase #2 $118.35   13.658%   $134.5142   $134.51   $134.50   $134.50  
  Purchase #3 $8.68   12.466%   $9.762   $9.76   $9.75   $9.80  
  Purchase #4 $250.93   3.768%   $260.385   $260.39   $260.40   $260.40  
  Purchase #5 $22.70   6.293%   $24.1285   $24.13   $24.15   $24.10  
  Purchase #6 $128.78   5.317%   $135.6272   $135.63   $135.65   $135.60  
  Purchase #7 $204.27   10.373%   $225.4589   $225.46   $225.45   $225.50  
  7 purchase totals = $798.54       $859.5603   $859.56   $859.60   $859.60