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 $87.99   6.395%   $93.617   $93.62   $93.60   $93.60  
  Purchase #2 $226.86   4.375%   $236.7851   $236.79   $236.80   $236.80  
  Purchase #3 $162.58   7.773%   $175.2173   $175.22   $175.20   $175.20  
  Purchase #4 $235.66   6.548%   $251.091   $251.09   $251.10   $251.10  
  Purchase #5 $102.51   11.155%   $113.945   $113.95   $113.95   $113.90  
  Purchase #6 $80.72   4.689%   $84.505   $84.51   $84.50   $84.50  
  Purchase #7 $206.48   5.373%   $217.5742   $217.57   $217.55   $217.60  
  7 purchase totals = $1,102.80       $1,172.7346   $1,172.75   $1,172.70   $1,172.70