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 $107.55   9.469%   $117.7339   $117.73   $117.75   $117.70  
  Purchase #2 $83.42   4.116%   $86.8536   $86.85   $86.85   $86.90  
  Purchase #3 $155.88   4.839%   $163.423   $163.42   $163.40   $163.40  
  Purchase #4 $135.86   4.850%   $142.4492   $142.45   $142.45   $142.40  
  Purchase #5 $33.40   4.129%   $34.7791   $34.78   $34.80   $34.80  
  Purchase #6 $157.26   6.206%   $167.0196   $167.02   $167.00   $167.00  
  Purchase #7 $182.44   10.746%   $202.045   $202.05   $202.05   $202.00  
  7 purchase totals = $855.81       $914.3034   $914.30   $914.30   $914.20