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 $160.99   13.268%   $182.3502   $182.35   $182.35   $182.40  
  Purchase #2 $30.99   6.485%   $32.9997   $33.00   $33.00   $33.00  
  Purchase #3 $234.99   8.118%   $254.0665   $254.07   $254.05   $254.10  
  Purchase #4 $88.32   8.518%   $95.8431   $95.84   $95.85   $95.80  
  Purchase #5 $245.98   7.752%   $265.0484   $265.05   $265.05   $265.00  
  Purchase #6 $18.59   8.866%   $20.2382   $20.24   $20.25   $20.20  
  Purchase #7 $103.44   7.759%   $111.4659   $111.47   $111.45   $111.50  
  7 purchase totals = $883.30       $962.0120   $962.02   $962.00   $962.00