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 $175.84   13.652%   $199.8457   $199.85   $199.85   $199.80  
  Purchase #2 $221.79   11.658%   $247.6463   $247.65   $247.65   $247.60  
  Purchase #3 $132.85   8.599%   $144.2738   $144.27   $144.25   $144.30  
  Purchase #4 $100.94   12.303%   $113.3586   $113.36   $113.35   $113.40  
  Purchase #5 $181.66   3.452%   $187.9309   $187.93   $187.95   $187.90  
  Purchase #6 $228.75   10.227%   $252.1443   $252.14   $252.15   $252.10  
  Purchase #7 $52.72   11.389%   $58.7243   $58.72   $58.70   $58.70  
  7 purchase totals = $1,094.55       $1,203.9239   $1,203.92   $1,203.90   $1,203.80