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 $240.92   11.736%   $269.1944   $269.19   $269.20   $269.20  
  Purchase #2 $46.86   12.210%   $52.5816   $52.58   $52.60   $52.60  
  Purchase #3 $162.75   8.156%   $176.0239   $176.02   $176.00   $176.00  
  Purchase #4 $84.76   6.521%   $90.2872   $90.29   $90.30   $90.30  
  Purchase #5 $238.67   5.201%   $251.0832   $251.08   $251.10   $251.10  
  Purchase #6 $247.41   4.118%   $257.5983   $257.60   $257.60   $257.60  
  Purchase #7 $236.58   5.647%   $249.9397   $249.94   $249.95   $249.90  
  7 purchase totals = $1,257.95       $1,346.7083   $1,346.70   $1,346.75   $1,346.70