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 $184.85   12.500%   $207.9563   $207.96   $207.95   $208.00  
  Purchase #2 $84.80   11.290%   $94.3739   $94.37   $94.35   $94.40  
  Purchase #3 $227.97   7.702%   $245.5282   $245.53   $245.55   $245.50  
  Purchase #4 $106.96   12.504%   $120.3343   $120.33   $120.35   $120.30  
  Purchase #5 $202.33   3.131%   $208.665   $208.67   $208.65   $208.70  
  Purchase #6 $30.85   11.561%   $34.4166   $34.42   $34.40   $34.40  
  Purchase #7 $24.83   5.668%   $26.2374   $26.24   $26.25   $26.20  
  7 purchase totals = $862.59       $937.5117   $937.52   $937.50   $937.50