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 $169.58   8.421%   $183.8603   $183.86   $183.85   $183.90  
  Purchase #2 $176.33   10.460%   $194.7741   $194.77   $194.75   $194.80  
  Purchase #3 $119.41   7.173%   $127.9753   $127.98   $128.00   $128.00  
  Purchase #4 $207.43   3.436%   $214.5573   $214.56   $214.55   $214.60  
  Purchase #5 $212.98   5.640%   $224.9921   $224.99   $225.00   $225.00  
  Purchase #6 $105.64   7.401%   $113.4584   $113.46   $113.45   $113.50  
  Purchase #7 $195.63   11.331%   $217.7968   $217.80   $217.80   $217.80  
  7 purchase totals = $1,187.00       $1,277.4143   $1,277.42   $1,277.40   $1,277.60