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 $113.76   12.298%   $127.7502   $127.75   $127.75   $127.80  
  Purchase #2 $250.44   11.405%   $279.0027   $279.00   $279.00   $279.00  
  Purchase #3 $211.58   4.462%   $221.0207   $221.02   $221.00   $221.00  
  Purchase #4 $40.65   6.790%   $43.4101   $43.41   $43.40   $43.40  
  Purchase #5 $77.49   9.147%   $84.578   $84.58   $84.60   $84.60  
  Purchase #6 $219.65   12.572%   $247.2644   $247.26   $247.25   $247.30  
  Purchase #7 $223.69   10.691%   $247.6047   $247.60   $247.60   $247.60  
  7 purchase totals = $1,137.26       $1,250.6308   $1,250.62   $1,250.60   $1,250.70