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 $24.61   7.430%   $26.4385   $26.44   $26.45   $26.40  
  Purchase #2 $173.49   10.258%   $191.2866   $191.29   $191.30   $191.30  
  Purchase #3 $245.31   12.686%   $276.43   $276.43   $276.45   $276.40  
  Purchase #4 $32.31   10.815%   $35.8043   $35.80   $35.80   $35.80  
  Purchase #5 $119.27   9.362%   $130.4361   $130.44   $130.45   $130.40  
  Purchase #6 $153.26   6.573%   $163.3338   $163.33   $163.35   $163.30  
  Purchase #7 $225.25   9.696%   $247.0902   $247.09   $247.10   $247.10  
  7 purchase totals = $973.50       $1,070.8195   $1,070.82   $1,070.90   $1,070.70