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 $24.36   8.621%   $26.4601   $26.46   $26.45   $26.50  
  Purchase #2 $180.53   11.694%   $201.6412   $201.64   $201.65   $201.60  
  Purchase #3 $44.54   6.416%   $47.3977   $47.40   $47.40   $47.40  
  Purchase #4 $185.56   12.485%   $208.7272   $208.73   $208.75   $208.70  
  Purchase #5 $244.86   12.662%   $275.8642   $275.86   $275.85   $275.90  
  Purchase #6 $189.85   5.779%   $200.8214   $200.82   $200.80   $200.80  
  Purchase #7 $38.98   3.459%   $40.3283   $40.33   $40.35   $40.30  
  7 purchase totals = $908.68       $1,001.2401   $1,001.24   $1,001.25   $1,001.20