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 $243.44   4.134%   $253.5038   $253.50   $253.50   $253.50  
  Purchase #2 $120.72   13.112%   $136.5488   $136.55   $136.55   $136.50  
  Purchase #3 $245.32   6.865%   $262.1612   $262.16   $262.15   $262.20  
  Purchase #4 $157.47   12.269%   $176.79   $176.79   $176.80   $176.80  
  Purchase #5 $235.65   4.605%   $246.5017   $246.50   $246.50   $246.50  
  Purchase #6 $147.76   12.473%   $166.1901   $166.19   $166.20   $166.20  
  Purchase #7 $226.69   6.490%   $241.4022   $241.40   $241.40   $241.40  
  7 purchase totals = $1,377.05       $1,483.0978   $1,483.09   $1,483.10   $1,483.10