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 $151.68   6.596%   $161.6848   $161.68   $161.70   $161.70  
  Purchase #2 $237.74   6.622%   $253.4831   $253.48   $253.50   $253.50  
  Purchase #3 $129.65   4.307%   $135.234   $135.23   $135.25   $135.20  
  Purchase #4 $87.91   6.157%   $93.3226   $93.32   $93.30   $93.30  
  Purchase #5 $159.35   3.583%   $165.0595   $165.06   $165.05   $165.10  
  Purchase #6 $173.71   5.802%   $183.7887   $183.79   $183.80   $183.80  
  Purchase #7 $211.56   3.871%   $219.7495   $219.75   $219.75   $219.70  
  7 purchase totals = $1,151.60       $1,212.3222   $1,212.31   $1,212.35   $1,212.30