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 $84.78   12.115%   $95.0511   $95.05   $95.05   $95.10  
  Purchase #2 $246.82   8.212%   $267.0889   $267.09   $267.10   $267.10  
  Purchase #3 $211.39   13.725%   $240.4033   $240.40   $240.40   $240.40  
  Purchase #4 $25.33   8.231%   $27.4149   $27.41   $27.40   $27.40  
  Purchase #5 $240.60   13.302%   $272.6046   $272.60   $272.60   $272.60  
  Purchase #6 $135.35   5.260%   $142.4694   $142.47   $142.45   $142.50  
  Purchase #7 $110.75   10.697%   $122.5969   $122.60   $122.60   $122.60  
  7 purchase totals = $1,055.02       $1,167.6291   $1,167.62   $1,167.60   $1,167.70