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 $243.55   8.490%   $264.2274   $264.23   $264.25   $264.20  
  Purchase #2 $162.53   11.690%   $181.5298   $181.53   $181.55   $181.50  
  Purchase #3 $198.43   4.217%   $206.7978   $206.80   $206.80   $206.80  
  Purchase #4 $193.45   8.791%   $210.4562   $210.46   $210.45   $210.50  
  Purchase #5 $245.25   10.249%   $270.3857   $270.39   $270.40   $270.40  
  Purchase #6 $54.42   7.717%   $58.6196   $58.62   $58.60   $58.60  
  Purchase #7 $199.33   7.462%   $214.204   $214.20   $214.20   $214.20  
  7 purchase totals = $1,296.96       $1,406.2205   $1,406.23   $1,406.25   $1,406.20