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 $140.87   7.660%   $151.6606   $151.66   $151.65   $151.70  
  Purchase #2 $198.55   13.631%   $225.6144   $225.61   $225.60   $225.60  
  Purchase #3 $55.72   12.716%   $62.8054   $62.81   $62.80   $62.80  
  Purchase #4 $230.28   9.516%   $252.1934   $252.19   $252.20   $252.20  
  Purchase #5 $18.25   10.591%   $20.1829   $20.18   $20.20   $20.20  
  Purchase #6 $119.89   6.175%   $127.2932   $127.29   $127.30   $127.30  
  Purchase #7 $103.44   3.284%   $106.837   $106.84   $106.85   $106.80  
  7 purchase totals = $867.00       $946.5869   $946.58   $946.60   $946.60