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 $113.49   10.283%   $125.1602   $125.16   $125.15   $125.20  
  Purchase #2 $99.34   13.236%   $112.4886   $112.49   $112.50   $112.50  
  Purchase #3 $44.25   11.436%   $49.3104   $49.31   $49.30   $49.30  
  Purchase #4 $187.56   13.748%   $213.3457   $213.35   $213.35   $213.30  
  Purchase #5 $175.64   9.642%   $192.5752   $192.58   $192.60   $192.60  
  Purchase #6 $197.37   7.416%   $212.007   $212.01   $212.00   $212.00  
  Purchase #7 $109.43   8.361%   $118.5794   $118.58   $118.60   $118.60  
  7 purchase totals = $927.08       $1,023.4665   $1,023.48   $1,023.50   $1,023.50