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 $194.94   4.111%   $202.954   $202.95   $202.95   $203.00  
  Purchase #2 $82.48   10.729%   $91.3293   $91.33   $91.35   $91.30  
  Purchase #3 $152.95   6.262%   $162.5277   $162.53   $162.55   $162.50  
  Purchase #4 $117.41   11.694%   $131.1399   $131.14   $131.15   $131.10  
  Purchase #5 $234.28   9.812%   $257.2676   $257.27   $257.25   $257.30  
  Purchase #6 $238.92   8.424%   $259.0466   $259.05   $259.05   $259.00  
  Purchase #7 $229.76   4.318%   $239.681   $239.68   $239.70   $239.70  
  7 purchase totals = $1,250.74       $1,343.9461   $1,343.95   $1,344.00   $1,343.90