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 $126.37   6.473%   $134.5499   $134.55   $134.55   $134.50  
  Purchase #2 $184.84   13.804%   $210.3553   $210.36   $210.35   $210.40  
  Purchase #3 $201.66   4.184%   $210.0975   $210.10   $210.10   $210.10  
  Purchase #4 $225.85   3.559%   $233.888   $233.89   $233.90   $233.90  
  Purchase #5 $72.91   8.861%   $79.3706   $79.37   $79.35   $79.40  
  Purchase #6 $48.51   13.445%   $55.0322   $55.03   $55.05   $55.00  
  Purchase #7 $135.90   5.203%   $142.9709   $142.97   $142.95   $143.00  
  7 purchase totals = $996.04       $1,066.2644   $1,066.27   $1,066.25   $1,066.30