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 $188.55   6.599%   $200.9924   $200.99   $201.00   $201.00  
  Purchase #2 $145.58   9.661%   $159.6445   $159.64   $159.65   $159.60  
  Purchase #3 $205.99   12.830%   $232.4185   $232.42   $232.40   $232.40  
  Purchase #4 $26.85   10.508%   $29.6714   $29.67   $29.65   $29.70  
  Purchase #5 $211.59   12.225%   $237.4569   $237.46   $237.45   $237.50  
  Purchase #6 $143.54   9.587%   $157.3012   $157.30   $157.30   $157.30  
  Purchase #7 $41.34   8.543%   $44.8717   $44.87   $44.85   $44.90  
  7 purchase totals = $963.44       $1,062.3566   $1,062.35   $1,062.30   $1,062.40