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 $121.87   3.651%   $126.3195   $126.32   $126.30   $126.30  
  Purchase #2 $167.37   8.308%   $181.2751   $181.28   $181.30   $181.30  
  Purchase #3 $214.80   7.774%   $231.4986   $231.50   $231.50   $231.50  
  Purchase #4 $200.36   6.446%   $213.2752   $213.28   $213.30   $213.30  
  Purchase #5 $220.25   8.568%   $239.121   $239.12   $239.10   $239.10  
  Purchase #6 $207.49   11.256%   $230.8451   $230.85   $230.85   $230.80  
  Purchase #7 $42.73   13.679%   $48.575   $48.58   $48.60   $48.60  
  7 purchase totals = $1,174.87       $1,270.9095   $1,270.93   $1,270.95   $1,270.90