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 $85.51   11.752%   $95.5591   $95.56   $95.55   $95.60  
  Purchase #2 $40.94   11.322%   $45.5752   $45.58   $45.60   $45.60  
  Purchase #3 $78.25   13.271%   $88.6346   $88.63   $88.65   $88.60  
  Purchase #4 $133.74   3.249%   $138.0852   $138.09   $138.10   $138.10  
  Purchase #5 $245.94   8.871%   $267.7573   $267.76   $267.75   $267.80  
  Purchase #6 $170.75   5.210%   $179.6461   $179.65   $179.65   $179.60  
  Purchase #7 $169.81   8.843%   $184.8263   $184.83   $184.85   $184.80  
  7 purchase totals = $924.94       $1,000.0838   $1,000.10   $1,000.15   $1,000.10