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 $56.54   3.416%   $58.4714   $58.47   $58.45   $58.50  
  Purchase #2 $182.77   7.630%   $196.7154   $196.72   $196.70   $196.70  
  Purchase #3 $168.79   4.479%   $176.3501   $176.35   $176.35   $176.40  
  Purchase #4 $14.51   4.848%   $15.2134   $15.21   $15.20   $15.20  
  Purchase #5 $196.35   3.178%   $202.59   $202.59   $202.60   $202.60  
  Purchase #6 $47.43   10.297%   $52.3139   $52.31   $52.30   $52.30  
  Purchase #7 $174.97   10.847%   $193.949   $193.95   $193.95   $193.90  
  7 purchase totals = $841.36       $895.6032   $895.60   $895.55   $895.60