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 $115.65   8.595%   $125.5901   $125.59   $125.60   $125.60  
  Purchase #2 $160.35   13.374%   $181.7952   $181.80   $181.80   $181.80  
  Purchase #3 $15.52   13.691%   $17.6448   $17.64   $17.65   $17.60  
  Purchase #4 $130.82   7.547%   $140.693   $140.69   $140.70   $140.70  
  Purchase #5 $240.38   12.534%   $270.5092   $270.51   $270.50   $270.50  
  Purchase #6 $50.63   9.335%   $55.3563   $55.36   $55.35   $55.40  
  Purchase #7 $228.67   4.766%   $239.5684   $239.57   $239.55   $239.60  
  7 purchase totals = $942.02       $1,031.1570   $1,031.16   $1,031.15   $1,031.20