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 $246.98   12.174%   $277.0473   $277.05   $277.05   $277.00  
  Purchase #2 $188.82   10.514%   $208.6725   $208.67   $208.65   $208.70  
  Purchase #3 $192.39   7.375%   $206.5788   $206.58   $206.60   $206.60  
  Purchase #4 $162.35   9.228%   $177.3317   $177.33   $177.35   $177.30  
  Purchase #5 $33.73   8.804%   $36.6996   $36.70   $36.70   $36.70  
  Purchase #6 $37.96   4.774%   $39.7722   $39.77   $39.75   $39.80  
  Purchase #7 $180.73   5.657%   $190.9539   $190.95   $190.95   $191.00  
  7 purchase totals = $1,042.96       $1,137.0560   $1,137.05   $1,137.05   $1,137.10