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 $67.58   13.502%   $76.7047   $76.70   $76.70   $76.70  
  Purchase #2 $23.81   12.719%   $26.8384   $26.84   $26.85   $26.80  
  Purchase #3 $237.38   11.137%   $263.817   $263.82   $263.80   $263.80  
  Purchase #4 $54.72   13.176%   $61.9299   $61.93   $61.95   $61.90  
  Purchase #5 $6.73   3.790%   $6.9851   $6.99   $7.00   $7.00  
  Purchase #6 $57.79   3.323%   $59.7104   $59.71   $59.70   $59.70  
  Purchase #7 $156.75   12.349%   $176.1071   $176.11   $176.10   $176.10  
  7 purchase totals = $604.76       $672.0926   $672.10   $672.10   $672.00