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 $115.40   3.761%   $119.7402   $119.74   $119.75   $119.70  
  Purchase #2 $177.38   11.616%   $197.9845   $197.98   $198.00   $198.00  
  Purchase #3 $167.26   9.616%   $183.3437   $183.34   $183.35   $183.30  
  Purchase #4 $80.79   13.631%   $91.8025   $91.80   $91.80   $91.80  
  Purchase #5 $227.49   7.444%   $244.4244   $244.42   $244.40   $244.40  
  Purchase #6 $127.61   6.648%   $136.0935   $136.09   $136.10   $136.10  
  Purchase #7 $216.25   6.624%   $230.5744   $230.57   $230.55   $230.60  
  7 purchase totals = $1,112.18       $1,203.9632   $1,203.94   $1,203.95   $1,203.90