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 $125.99   5.254%   $132.6095   $132.61   $132.60   $132.60  
  Purchase #2 $211.36   12.744%   $238.2957   $238.30   $238.30   $238.30  
  Purchase #3 $15.41   4.718%   $16.137   $16.14   $16.15   $16.10  
  Purchase #4 $175.25   9.507%   $191.911   $191.91   $191.90   $191.90  
  Purchase #5 $230.68   5.787%   $244.0295   $244.03   $244.05   $244.00  
  Purchase #6 $196.88   8.113%   $212.8529   $212.85   $212.85   $212.90  
  Purchase #7 $16.35   13.495%   $18.5564   $18.56   $18.55   $18.60  
  7 purchase totals = $971.92       $1,054.3920   $1,054.40   $1,054.40   $1,054.40