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 $191.92   4.396%   $200.3568   $200.36   $200.35   $200.40  
  Purchase #2 $49.81   13.351%   $56.4601   $56.46   $56.45   $56.50  
  Purchase #3 $140.33   9.408%   $153.5322   $153.53   $153.55   $153.50  
  Purchase #4 $126.51   5.366%   $133.2985   $133.30   $133.30   $133.30  
  Purchase #5 $92.51   3.386%   $95.6424   $95.64   $95.65   $95.60  
  Purchase #6 $168.56   10.586%   $186.4038   $186.40   $186.40   $186.40  
  Purchase #7 $189.69   8.572%   $205.9502   $205.95   $205.95   $206.00  
  7 purchase totals = $959.33       $1,031.6440   $1,031.64   $1,031.65   $1,031.70