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 $196.29   5.569%   $207.2214   $207.22   $207.20   $207.20  
  Purchase #2 $227.36   9.164%   $248.1953   $248.20   $248.20   $248.20  
  Purchase #3 $250.66   6.664%   $267.364   $267.36   $267.35   $267.40  
  Purchase #4 $249.96   5.373%   $263.3904   $263.39   $263.40   $263.40  
  Purchase #5 $37.28   13.618%   $42.3568   $42.36   $42.35   $42.40  
  Purchase #6 $93.60   5.729%   $98.9623   $98.96   $98.95   $99.00  
  Purchase #7 $196.47   5.260%   $206.8043   $206.80   $206.80   $206.80  
  7 purchase totals = $1,251.62       $1,334.2945   $1,334.29   $1,334.25   $1,334.40