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 $194.66   7.377%   $209.0201   $209.02   $209.00   $209.00  
  Purchase #2 $150.90   5.357%   $158.9837   $158.98   $159.00   $159.00  
  Purchase #3 $161.89   9.731%   $177.6435   $177.64   $177.65   $177.60  
  Purchase #4 $120.90   8.694%   $131.411   $131.41   $131.40   $131.40  
  Purchase #5 $23.41   12.525%   $26.3421   $26.34   $26.35   $26.30  
  Purchase #6 $168.74   9.438%   $184.6657   $184.67   $184.65   $184.70  
  Purchase #7 $162.69   12.649%   $183.2687   $183.27   $183.25   $183.30  
  7 purchase totals = $983.19       $1,071.3348   $1,071.33   $1,071.30   $1,071.30