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 $55.76   11.153%   $61.9789   $61.98   $62.00   $62.00  
  Purchase #2 $82.32   7.236%   $88.2767   $88.28   $88.30   $88.30  
  Purchase #3 $136.86   13.417%   $155.2225   $155.22   $155.20   $155.20  
  Purchase #4 $245.51   11.701%   $274.2371   $274.24   $274.25   $274.20  
  Purchase #5 $183.44   12.177%   $205.7775   $205.78   $205.80   $205.80  
  Purchase #6 $227.42   7.813%   $245.1883   $245.19   $245.20   $245.20  
  Purchase #7 $84.99   13.527%   $96.4866   $96.49   $96.50   $96.50  
  7 purchase totals = $1,016.30       $1,127.1676   $1,127.18   $1,127.25   $1,127.20