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 $187.92   12.621%   $211.6374   $211.64   $211.65   $211.60  
  Purchase #2 $151.73   9.455%   $166.0761   $166.08   $166.10   $166.10  
  Purchase #3 $48.66   10.649%   $53.8418   $53.84   $53.85   $53.80  
  Purchase #4 $142.53   12.142%   $159.836   $159.84   $159.85   $159.80  
  Purchase #5 $85.73   12.162%   $96.1565   $96.16   $96.15   $96.20  
  Purchase #6 $160.28   10.857%   $177.6816   $177.68   $177.70   $177.70  
  Purchase #7 $97.37   7.201%   $104.3816   $104.38   $104.40   $104.40  
  7 purchase totals = $874.22       $969.6110   $969.62   $969.70   $969.60