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 $111.58   13.611%   $126.7672   $126.77   $126.75   $126.80  
  Purchase #2 $248.31   3.644%   $257.3584   $257.36   $257.35   $257.40  
  Purchase #3 $26.32   6.820%   $28.115   $28.12   $28.10   $28.10  
  Purchase #4 $39.33   4.521%   $41.1081   $41.11   $41.10   $41.10  
  Purchase #5 $233.80   5.300%   $246.1914   $246.19   $246.20   $246.20  
  Purchase #6 $63.94   3.411%   $66.121   $66.12   $66.10   $66.10  
  Purchase #7 $39.45   12.501%   $44.3816   $44.38   $44.40   $44.40  
  7 purchase totals = $762.73       $810.0427   $810.05   $810.00   $810.10