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 $150.26   8.654%   $163.2635   $163.26   $163.25   $163.30  
  Purchase #2 $239.47   11.628%   $267.3156   $267.32   $267.30   $267.30  
  Purchase #3 $77.83   7.550%   $83.7062   $83.71   $83.70   $83.70  
  Purchase #4 $48.60   4.215%   $50.6485   $50.65   $50.65   $50.60  
  Purchase #5 $197.84   12.310%   $222.1941   $222.19   $222.20   $222.20  
  Purchase #6 $230.31   8.241%   $249.2898   $249.29   $249.30   $249.30  
  Purchase #7 $233.27   11.204%   $259.4056   $259.41   $259.40   $259.40  
  7 purchase totals = $1,177.58       $1,295.8233   $1,295.83   $1,295.80   $1,295.80