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 $64.86   13.724%   $73.7614   $73.76   $73.75   $73.80  
  Purchase #2 $153.66   8.423%   $166.6028   $166.60   $166.60   $166.60  
  Purchase #3 $180.66   6.244%   $191.9404   $191.94   $191.95   $191.90  
  Purchase #4 $111.46   8.508%   $120.943   $120.94   $120.95   $120.90  
  Purchase #5 $209.51   6.649%   $223.4403   $223.44   $223.45   $223.40  
  Purchase #6 $180.57   4.730%   $189.111   $189.11   $189.10   $189.10  
  Purchase #7 $178.74   5.810%   $189.1248   $189.12   $189.10   $189.10  
  7 purchase totals = $1,079.46       $1,154.9237   $1,154.91   $1,154.90   $1,154.80