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 $162.33   6.849%   $173.448   $173.45   $173.45   $173.40  
  Purchase #2 $219.70   3.484%   $227.3543   $227.35   $227.35   $227.40  
  Purchase #3 $161.29   8.731%   $175.3722   $175.37   $175.35   $175.40  
  Purchase #4 $95.65   13.425%   $108.491   $108.49   $108.50   $108.50  
  Purchase #5 $233.65   12.746%   $263.431   $263.43   $263.45   $263.40  
  Purchase #6 $187.75   5.871%   $198.7728   $198.77   $198.75   $198.80  
  Purchase #7 $96.74   10.306%   $106.71   $106.71   $106.70   $106.70  
  7 purchase totals = $1,157.11       $1,253.5793   $1,253.57   $1,253.55   $1,253.60