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 $210.32   13.771%   $239.2832   $239.28   $239.30   $239.30  
  Purchase #2 $144.83   7.447%   $155.6155   $155.62   $155.60   $155.60  
  Purchase #3 $155.47   6.541%   $165.6393   $165.64   $165.65   $165.60  
  Purchase #4 $191.42   6.281%   $203.4431   $203.44   $203.45   $203.40  
  Purchase #5 $162.41   13.772%   $184.7771   $184.78   $184.80   $184.80  
  Purchase #6 $220.31   11.478%   $245.5972   $245.60   $245.60   $245.60  
  Purchase #7 $66.40   8.487%   $72.0354   $72.04   $72.05   $72.00  
  7 purchase totals = $1,151.16       $1,266.3908   $1,266.40   $1,266.45   $1,266.30