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 $207.30   7.313%   $222.4598   $222.46   $222.45   $222.50  
  Purchase #2 $108.85   6.645%   $116.0831   $116.08   $116.10   $116.10  
  Purchase #3 $137.46   5.570%   $145.1165   $145.12   $145.10   $145.10  
  Purchase #4 $75.34   5.133%   $79.2072   $79.21   $79.20   $79.20  
  Purchase #5 $28.84   7.585%   $31.0275   $31.03   $31.05   $31.00  
  Purchase #6 $47.46   3.515%   $49.1282   $49.13   $49.15   $49.10  
  Purchase #7 $22.37   5.520%   $23.6048   $23.60   $23.60   $23.60  
  7 purchase totals = $627.62       $666.6271   $666.63   $666.65   $666.60