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 $31.82   5.441%   $33.5513   $33.55   $33.55   $33.60  
  Purchase #2 $151.79   7.670%   $163.4323   $163.43   $163.45   $163.40  
  Purchase #3 $65.89   8.445%   $71.4544   $71.45   $71.45   $71.50  
  Purchase #4 $89.72   6.742%   $95.7689   $95.77   $95.75   $95.80  
  Purchase #5 $195.80   9.253%   $213.9174   $213.92   $213.90   $213.90  
  Purchase #6 $25.55   10.159%   $28.1456   $28.15   $28.15   $28.10  
  Purchase #7 $66.86   3.262%   $69.041   $69.04   $69.05   $69.00  
  7 purchase totals = $627.43       $675.3109   $675.31   $675.30   $675.30