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 $119.66   8.740%   $130.1183   $130.12   $130.10   $130.10  
  Purchase #2 $100.75   7.554%   $108.3607   $108.36   $108.35   $108.40  
  Purchase #3 $147.68   4.549%   $154.398   $154.40   $154.40   $154.40  
  Purchase #4 $60.84   7.185%   $65.2114   $65.21   $65.20   $65.20  
  Purchase #5 $166.96   9.762%   $183.2586   $183.26   $183.25   $183.30  
  Purchase #6 $26.48   3.170%   $27.3194   $27.32   $27.30   $27.30  
  Purchase #7 $122.94   8.260%   $133.0948   $133.09   $133.10   $133.10  
  7 purchase totals = $745.31       $801.7612   $801.76   $801.70   $801.80