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 $134.86   13.365%   $152.884   $152.88   $152.90   $152.90  
  Purchase #2 $96.68   8.532%   $104.9287   $104.93   $104.95   $104.90  
  Purchase #3 $239.89   8.207%   $259.5778   $259.58   $259.60   $259.60  
  Purchase #4 $11.50   9.102%   $12.5467   $12.55   $12.55   $12.50  
  Purchase #5 $211.95   6.464%   $225.6504   $225.65   $225.65   $225.70  
  Purchase #6 $157.25   11.446%   $175.2488   $175.25   $175.25   $175.20  
  Purchase #7 $122.88   9.449%   $134.4909   $134.49   $134.50   $134.50  
  7 purchase totals = $975.01       $1,065.3273   $1,065.33   $1,065.40   $1,065.30