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 $41.58   12.402%   $46.7368   $46.74   $46.75   $46.70  
  Purchase #2 $180.49   13.779%   $205.3597   $205.36   $205.35   $205.40  
  Purchase #3 $166.37   9.555%   $182.2667   $182.27   $182.25   $182.30  
  Purchase #4 $98.69   10.236%   $108.7919   $108.79   $108.80   $108.80  
  Purchase #5 $28.64   3.245%   $29.5694   $29.57   $29.55   $29.60  
  Purchase #6 $145.58   6.841%   $155.5391   $155.54   $155.55   $155.50  
  Purchase #7 $244.71   8.553%   $265.64   $265.64   $265.65   $265.60  
  7 purchase totals = $906.06       $993.9036   $993.91   $993.90   $993.90