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 $213.65   10.481%   $236.0427   $236.04   $236.05   $236.00  
  Purchase #2 $82.51   3.732%   $85.5893   $85.59   $85.60   $85.60  
  Purchase #3 $34.42   6.681%   $36.7196   $36.72   $36.70   $36.70  
  Purchase #4 $133.82   8.412%   $145.0769   $145.08   $145.10   $145.10  
  Purchase #5 $132.97   7.391%   $142.7978   $142.80   $142.80   $142.80  
  Purchase #6 $194.84   4.217%   $203.0564   $203.06   $203.05   $203.10  
  Purchase #7 $118.96   11.803%   $133.0008   $133.00   $133.00   $133.00  
  7 purchase totals = $911.17       $982.2835   $982.29   $982.30   $982.30