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 $43.74   3.829%   $45.4148   $45.41   $45.40   $45.40  
  Purchase #2 $71.58   13.630%   $81.3364   $81.34   $81.35   $81.30  
  Purchase #3 $162.47   9.558%   $177.9989   $178.00   $178.00   $178.00  
  Purchase #4 $222.60   9.317%   $243.3396   $243.34   $243.35   $243.30  
  Purchase #5 $7.44   4.136%   $7.7477   $7.75   $7.75   $7.70  
  Purchase #6 $77.26   3.789%   $80.1874   $80.19   $80.20   $80.20  
  Purchase #7 $30.50   8.155%   $32.9873   $32.99   $33.00   $33.00  
  7 purchase totals = $615.59       $669.0121   $669.02   $669.05   $668.90