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 $106.72   8.374%   $115.6567   $115.66   $115.65   $115.70  
  Purchase #2 $58.62   11.149%   $65.1555   $65.16   $65.15   $65.20  
  Purchase #3 $162.73   8.111%   $175.929   $175.93   $175.95   $175.90  
  Purchase #4 $43.64   11.312%   $48.5766   $48.58   $48.60   $48.60  
  Purchase #5 $54.79   8.756%   $59.5874   $59.59   $59.60   $59.60  
  Purchase #6 $174.65   13.285%   $197.8523   $197.85   $197.85   $197.90  
  Purchase #7 $220.43   5.811%   $233.2392   $233.24   $233.25   $233.20  
  7 purchase totals = $821.58       $895.9967   $896.01   $896.05   $896.10