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 $119.25   13.770%   $135.6707   $135.67   $135.65   $135.70  
  Purchase #2 $15.43   8.365%   $16.7207   $16.72   $16.70   $16.70  
  Purchase #3 $203.86   7.208%   $218.5542   $218.55   $218.55   $218.60  
  Purchase #4 $238.42   5.642%   $251.8717   $251.87   $251.85   $251.90  
  Purchase #5 $196.92   12.180%   $220.9049   $220.90   $220.90   $220.90  
  Purchase #6 $229.49   7.831%   $247.4614   $247.46   $247.45   $247.50  
  Purchase #7 $225.37   10.658%   $249.3899   $249.39   $249.40   $249.40  
  7 purchase totals = $1,228.74       $1,340.5735   $1,340.56   $1,340.50   $1,340.70