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 $49.54   4.261%   $51.6509   $51.65   $51.65   $51.70  
  Purchase #2 $184.84   3.385%   $191.0968   $191.10   $191.10   $191.10  
  Purchase #3 $188.80   11.850%   $211.1728   $211.17   $211.15   $211.20  
  Purchase #4 $157.81   13.769%   $179.5389   $179.54   $179.55   $179.50  
  Purchase #5 $89.52   8.509%   $97.1373   $97.14   $97.15   $97.10  
  Purchase #6 $206.77   11.138%   $229.8   $229.80   $229.80   $229.80  
  Purchase #7 $99.95   13.600%   $113.5432   $113.54   $113.55   $113.50  
  7 purchase totals = $977.23       $1,073.9399   $1,073.94   $1,073.95   $1,073.90