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 $192.40   7.763%   $207.336   $207.34   $207.35   $207.30  
  Purchase #2 $37.48   9.456%   $41.0241   $41.02   $41.00   $41.00  
  Purchase #3 $243.54   7.460%   $261.7081   $261.71   $261.70   $261.70  
  Purchase #4 $40.26   4.472%   $42.0604   $42.06   $42.05   $42.10  
  Purchase #5 $212.47   7.771%   $228.981   $228.98   $229.00   $229.00  
  Purchase #6 $149.96   5.270%   $157.8629   $157.86   $157.85   $157.90  
  Purchase #7 $76.88   10.102%   $84.6464   $84.65   $84.65   $84.60  
  7 purchase totals = $952.99       $1,023.6189   $1,023.62   $1,023.60   $1,023.60