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 $232.60   9.874%   $255.5669   $255.57   $255.55   $255.60  
  Purchase #2 $188.41   3.135%   $194.3167   $194.32   $194.30   $194.30  
  Purchase #3 $167.30   3.183%   $172.6252   $172.63   $172.65   $172.60  
  Purchase #4 $59.57   12.424%   $66.971   $66.97   $66.95   $67.00  
  Purchase #5 $135.93   7.579%   $146.2321   $146.23   $146.25   $146.20  
  Purchase #6 $170.34   6.710%   $181.7698   $181.77   $181.75   $181.80  
  Purchase #7 $30.84   7.754%   $33.2313   $33.23   $33.25   $33.20  
  7 purchase totals = $984.99       $1,050.7130   $1,050.72   $1,050.70   $1,050.70