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 $69.40   6.535%   $73.9353   $73.94   $73.95   $73.90  
  Purchase #2 $60.80   3.604%   $62.9912   $62.99   $63.00   $63.00  
  Purchase #3 $206.43   6.226%   $219.2823   $219.28   $219.30   $219.30  
  Purchase #4 $69.77   6.472%   $74.2855   $74.29   $74.30   $74.30  
  Purchase #5 $93.75   6.600%   $99.9375   $99.94   $99.95   $99.90  
  Purchase #6 $16.37   11.270%   $18.2149   $18.21   $18.20   $18.20  
  Purchase #7 $189.68   5.804%   $200.689   $200.69   $200.70   $200.70  
  7 purchase totals = $706.20       $749.3357   $749.34   $749.40   $749.30