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 $228.88   7.865%   $246.8814   $246.88   $246.90   $246.90  
  Purchase #2 $158.85   11.572%   $177.2321   $177.23   $177.25   $177.20  
  Purchase #3 $228.42   4.773%   $239.3225   $239.32   $239.30   $239.30  
  Purchase #4 $88.29   8.358%   $95.6693   $95.67   $95.65   $95.70  
  Purchase #5 $43.52   5.781%   $46.0359   $46.04   $46.05   $46.00  
  Purchase #6 $247.85   3.869%   $257.4393   $257.44   $257.45   $257.40  
  Purchase #7 $221.65   7.853%   $239.0562   $239.06   $239.05   $239.10  
  7 purchase totals = $1,217.46       $1,301.6367   $1,301.64   $1,301.65   $1,301.60