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 $151.69   11.371%   $168.9387   $168.94   $168.95   $168.90  
  Purchase #2 $200.46   5.574%   $211.6336   $211.63   $211.65   $211.60  
  Purchase #3 $20.52   3.391%   $21.2158   $21.22   $21.20   $21.20  
  Purchase #4 $106.67   3.787%   $110.7096   $110.71   $110.70   $110.70  
  Purchase #5 $115.43   5.384%   $121.6448   $121.64   $121.65   $121.60  
  Purchase #6 $140.44   10.845%   $155.6707   $155.67   $155.65   $155.70  
  Purchase #7 $191.74   9.865%   $210.6552   $210.66   $210.65   $210.70  
  7 purchase totals = $926.95       $1,000.4684   $1,000.47   $1,000.45   $1,000.40