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 $100.32   3.488%   $103.8192   $103.82   $103.80   $103.80  
  Purchase #2 $223.30   10.579%   $246.9229   $246.92   $246.90   $246.90  
  Purchase #3 $243.84   3.691%   $252.8401   $252.84   $252.85   $252.80  
  Purchase #4 $34.75   8.835%   $37.8202   $37.82   $37.80   $37.80  
  Purchase #5 $145.49   6.354%   $154.7344   $154.73   $154.75   $154.70  
  Purchase #6 $12.56   10.624%   $13.8944   $13.89   $13.90   $13.90  
  Purchase #7 $95.94   11.758%   $107.2206   $107.22   $107.20   $107.20  
  7 purchase totals = $856.20       $917.2518   $917.24   $917.20   $917.10