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 $122.58   3.702%   $127.1179   $127.12   $127.10   $127.10  
  Purchase #2 $244.56   7.638%   $263.2395   $263.24   $263.25   $263.20  
  Purchase #3 $98.36   9.477%   $107.6816   $107.68   $107.70   $107.70  
  Purchase #4 $126.40   12.353%   $142.0142   $142.01   $142.00   $142.00  
  Purchase #5 $48.76   6.615%   $51.9855   $51.99   $52.00   $52.00  
  Purchase #6 $173.98   11.786%   $194.4853   $194.49   $194.50   $194.50  
  Purchase #7 $132.27   5.702%   $139.812   $139.81   $139.80   $139.80  
  7 purchase totals = $946.91       $1,026.3360   $1,026.34   $1,026.35   $1,026.30