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 $163.39   13.342%   $185.1895   $185.19   $185.20   $185.20  
  Purchase #2 $177.72   9.544%   $194.6816   $194.68   $194.70   $194.70  
  Purchase #3 $162.97   5.352%   $171.6922   $171.69   $171.70   $171.70  
  Purchase #4 $65.47   10.638%   $72.4347   $72.43   $72.45   $72.40  
  Purchase #5 $150.52   4.378%   $157.1098   $157.11   $157.10   $157.10  
  Purchase #6 $168.81   13.727%   $191.9825   $191.98   $192.00   $192.00  
  Purchase #7 $87.97   11.598%   $98.1728   $98.17   $98.15   $98.20  
  7 purchase totals = $976.85       $1,071.2631   $1,071.25   $1,071.30   $1,071.30