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 $196.92   3.112%   $203.0482   $203.05   $203.05   $203.00  
  Purchase #2 $80.61   12.542%   $90.7201   $90.72   $90.70   $90.70  
  Purchase #3 $214.42   8.873%   $233.4455   $233.45   $233.45   $233.40  
  Purchase #4 $191.33   6.363%   $203.5043   $203.50   $203.50   $203.50  
  Purchase #5 $218.88   3.629%   $226.8232   $226.82   $226.80   $226.80  
  Purchase #6 $197.70   4.854%   $207.2964   $207.30   $207.30   $207.30  
  Purchase #7 $36.65   6.231%   $38.9337   $38.93   $38.95   $38.90  
  7 purchase totals = $1,136.51       $1,203.7714   $1,203.77   $1,203.75   $1,203.60