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 $178.64   3.169%   $184.3011   $184.30   $184.30   $184.30  
  Purchase #2 $60.25   5.726%   $63.6999   $63.70   $63.70   $63.70  
  Purchase #3 $23.54   10.425%   $25.994   $25.99   $26.00   $26.00  
  Purchase #4 $89.62   6.331%   $95.2938   $95.29   $95.30   $95.30  
  Purchase #5 $157.34   11.706%   $175.7582   $175.76   $175.75   $175.80  
  Purchase #6 $164.85   8.810%   $179.3733   $179.37   $179.35   $179.40  
  Purchase #7 $218.98   11.580%   $244.3379   $244.34   $244.35   $244.30  
  7 purchase totals = $893.22       $968.7582   $968.75   $968.75   $968.80