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 $231.26   7.197%   $247.9038   $247.90   $247.90   $247.90  
  Purchase #2 $239.99   5.568%   $253.3526   $253.35   $253.35   $253.40  
  Purchase #3 $119.43   3.719%   $123.8716   $123.87   $123.85   $123.90  
  Purchase #4 $89.65   9.409%   $98.0852   $98.09   $98.10   $98.10  
  Purchase #5 $53.39   12.594%   $60.1139   $60.11   $60.10   $60.10  
  Purchase #6 $99.99   7.146%   $107.1353   $107.14   $107.15   $107.10  
  Purchase #7 $160.64   7.198%   $172.2029   $172.20   $172.20   $172.20  
  7 purchase totals = $994.35       $1,062.6653   $1,062.66   $1,062.65   $1,062.70