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 $215.97   7.841%   $232.9042   $232.90   $232.90   $232.90  
  Purchase #2 $145.38   5.760%   $153.7539   $153.75   $153.75   $153.80  
  Purchase #3 $61.58   6.165%   $65.3764   $65.38   $65.40   $65.40  
  Purchase #4 $229.48   13.432%   $260.3038   $260.30   $260.30   $260.30  
  Purchase #5 $75.69   8.874%   $82.4067   $82.41   $82.40   $82.40  
  Purchase #6 $176.90   9.382%   $193.4968   $193.50   $193.50   $193.50  
  Purchase #7 $178.59   8.662%   $194.0595   $194.06   $194.05   $194.10  
  7 purchase totals = $1,083.59       $1,182.3013   $1,182.30   $1,182.30   $1,182.40