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 $5.64   7.215%   $6.0469   $6.05   $6.05   $6.00  
  Purchase #2 $193.97   7.717%   $208.9387   $208.94   $208.95   $208.90  
  Purchase #3 $213.46   4.137%   $222.2908   $222.29   $222.30   $222.30  
  Purchase #4 $236.98   6.102%   $251.4405   $251.44   $251.45   $251.40  
  Purchase #5 $148.54   6.232%   $157.797   $157.80   $157.80   $157.80  
  Purchase #6 $127.29   3.170%   $131.3251   $131.33   $131.35   $131.30  
  Purchase #7 $46.61   4.803%   $48.8487   $48.85   $48.85   $48.80  
  7 purchase totals = $972.49       $1,026.6877   $1,026.70   $1,026.75   $1,026.50