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 $200.43   12.849%   $226.1833   $226.18   $226.20   $226.20  
  Purchase #2 $110.31   8.522%   $119.7106   $119.71   $119.70   $119.70  
  Purchase #3 $149.85   4.218%   $156.1707   $156.17   $156.15   $156.20  
  Purchase #4 $31.46   4.699%   $32.9383   $32.94   $32.95   $32.90  
  Purchase #5 $248.49   7.776%   $267.8126   $267.81   $267.80   $267.80  
  Purchase #6 $81.94   4.361%   $85.5134   $85.51   $85.50   $85.50  
  Purchase #7 $209.73   3.578%   $217.2341   $217.23   $217.25   $217.20  
  7 purchase totals = $1,032.21       $1,105.5630   $1,105.55   $1,105.55   $1,105.50