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 $184.34   5.147%   $193.828   $193.83   $193.85   $193.80  
  Purchase #2 $60.62   13.369%   $68.7243   $68.72   $68.70   $68.70  
  Purchase #3 $205.58   6.547%   $219.0393   $219.04   $219.05   $219.00  
  Purchase #4 $216.83   9.584%   $237.611   $237.61   $237.60   $237.60  
  Purchase #5 $210.50   5.624%   $222.3385   $222.34   $222.35   $222.30  
  Purchase #6 $85.69   8.337%   $92.834   $92.83   $92.85   $92.80  
  Purchase #7 $211.53   6.802%   $225.9183   $225.92   $225.90   $225.90  
  7 purchase totals = $1,175.09       $1,260.2934   $1,260.29   $1,260.30   $1,260.10