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 $135.73   8.592%   $147.3919   $147.39   $147.40   $147.40  
  Purchase #2 $59.42   4.129%   $61.8735   $61.87   $61.85   $61.90  
  Purchase #3 $55.89   4.641%   $58.4839   $58.48   $58.50   $58.50  
  Purchase #4 $219.83   11.247%   $244.5543   $244.55   $244.55   $244.60  
  Purchase #5 $75.70   8.393%   $82.0535   $82.05   $82.05   $82.10  
  Purchase #6 $178.71   10.255%   $197.0367   $197.04   $197.05   $197.00  
  Purchase #7 $161.44   3.747%   $167.4892   $167.49   $167.50   $167.50  
  7 purchase totals = $886.72       $958.8830   $958.87   $958.90   $959.00