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 $65.51   10.606%   $72.458   $72.46   $72.45   $72.50  
  Purchase #2 $236.67   7.337%   $254.0345   $254.03   $254.05   $254.00  
  Purchase #3 $55.39   11.823%   $61.9388   $61.94   $61.95   $61.90  
  Purchase #4 $31.36   13.849%   $35.703   $35.70   $35.70   $35.70  
  Purchase #5 $208.61   7.375%   $223.995   $224.00   $224.00   $224.00  
  Purchase #6 $123.45   13.784%   $140.4663   $140.47   $140.45   $140.50  
  Purchase #7 $229.65   5.365%   $241.9707   $241.97   $241.95   $242.00  
  7 purchase totals = $950.64       $1,030.5663   $1,030.57   $1,030.55   $1,030.60