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 $233.71   3.440%   $241.7496   $241.75   $241.75   $241.70  
  Purchase #2 $182.94   12.179%   $205.2203   $205.22   $205.20   $205.20  
  Purchase #3 $128.69   4.764%   $134.8208   $134.82   $134.80   $134.80  
  Purchase #4 $32.98   6.141%   $35.0053   $35.01   $35.00   $35.00  
  Purchase #5 $89.25   5.387%   $94.0579   $94.06   $94.05   $94.10  
  Purchase #6 $98.46   8.338%   $106.6696   $106.67   $106.65   $106.70  
  Purchase #7 $33.53   11.290%   $37.3155   $37.32   $37.30   $37.30  
  7 purchase totals = $799.56       $854.8390   $854.85   $854.75   $854.80