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 $119.59   3.109%   $123.3081   $123.31   $123.30   $123.30  
  Purchase #2 $168.34   3.707%   $174.5804   $174.58   $174.60   $174.60  
  Purchase #3 $239.32   8.427%   $259.4875   $259.49   $259.50   $259.50  
  Purchase #4 $245.84   9.454%   $269.0817   $269.08   $269.10   $269.10  
  Purchase #5 $124.83   12.642%   $140.611   $140.61   $140.60   $140.60  
  Purchase #6 $116.94   8.432%   $126.8004   $126.80   $126.80   $126.80  
  Purchase #7 $218.91   12.468%   $246.2037   $246.20   $246.20   $246.20  
  7 purchase totals = $1,233.77       $1,340.0728   $1,340.07   $1,340.10   $1,340.10