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 $119.38   6.680%   $127.3546   $127.35   $127.35   $127.40  
  Purchase #2 $185.41   9.668%   $203.3354   $203.34   $203.35   $203.30  
  Purchase #3 $59.99   8.553%   $65.1209   $65.12   $65.10   $65.10  
  Purchase #4 $115.63   4.344%   $120.653   $120.65   $120.65   $120.70  
  Purchase #5 $221.72   13.345%   $251.3085   $251.31   $251.30   $251.30  
  Purchase #6 $31.60   3.314%   $32.6472   $32.65   $32.65   $32.60  
  Purchase #7 $183.70   10.659%   $203.2806   $203.28   $203.30   $203.30  
  7 purchase totals = $917.43       $1,003.7002   $1,003.70   $1,003.70   $1,003.70