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 $111.57   13.781%   $126.9455   $126.95   $126.95   $126.90  
  Purchase #2 $223.44   4.198%   $232.82   $232.82   $232.80   $232.80  
  Purchase #3 $135.54   7.656%   $145.9169   $145.92   $145.90   $145.90  
  Purchase #4 $201.45   12.687%   $227.008   $227.01   $227.00   $227.00  
  Purchase #5 $53.51   13.852%   $60.9222   $60.92   $60.90   $60.90  
  Purchase #6 $152.67   5.154%   $160.5386   $160.54   $160.55   $160.50  
  Purchase #7 $145.59   3.720%   $151.0059   $151.01   $151.00   $151.00  
  7 purchase totals = $1,023.77       $1,105.1571   $1,105.17   $1,105.10   $1,105.00