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 $154.56   7.826%   $166.6559   $166.66   $166.65   $166.70  
  Purchase #2 $163.94   11.357%   $182.5587   $182.56   $182.55   $182.60  
  Purchase #3 $169.78   8.132%   $183.5865   $183.59   $183.60   $183.60  
  Purchase #4 $103.72   7.483%   $111.4814   $111.48   $111.50   $111.50  
  Purchase #5 $209.36   11.736%   $233.9305   $233.93   $233.95   $233.90  
  Purchase #6 $72.56   3.615%   $75.183   $75.18   $75.20   $75.20  
  Purchase #7 $234.64   13.814%   $267.0532   $267.05   $267.05   $267.10  
  7 purchase totals = $1,108.56       $1,220.4492   $1,220.45   $1,220.50   $1,220.60