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 $106.76   12.278%   $119.868   $119.87   $119.85   $119.90  
  Purchase #2 $157.91   8.245%   $170.9297   $170.93   $170.95   $170.90  
  Purchase #3 $221.56   9.366%   $242.3113   $242.31   $242.30   $242.30  
  Purchase #4 $158.46   8.453%   $171.8546   $171.85   $171.85   $171.90  
  Purchase #5 $153.91   8.719%   $167.3294   $167.33   $167.35   $167.30  
  Purchase #6 $244.95   11.334%   $272.7126   $272.71   $272.70   $272.70  
  Purchase #7 $9.27   4.586%   $9.6951   $9.70   $9.70   $9.70  
  7 purchase totals = $1,052.82       $1,154.7007   $1,154.70   $1,154.70   $1,154.70