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 $205.84   13.543%   $233.7169   $233.72   $233.70   $233.70  
  Purchase #2 $145.55   7.368%   $156.2741   $156.27   $156.25   $156.30  
  Purchase #3 $157.98   12.413%   $177.5901   $177.59   $177.60   $177.60  
  Purchase #4 $162.98   9.376%   $178.261   $178.26   $178.25   $178.30  
  Purchase #5 $205.63   5.285%   $216.4975   $216.50   $216.50   $216.50  
  Purchase #6 $175.49   11.779%   $196.161   $196.16   $196.15   $196.20  
  Purchase #7 $88.49   6.106%   $93.8932   $93.89   $93.90   $93.90  
  7 purchase totals = $1,141.96       $1,252.3938   $1,252.39   $1,252.35   $1,252.50