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 $74.37   11.583%   $82.9843   $82.98   $83.00   $83.00  
  Purchase #2 $176.89   13.572%   $200.8975   $200.90   $200.90   $200.90  
  Purchase #3 $230.76   3.565%   $238.9866   $238.99   $239.00   $239.00  
  Purchase #4 $126.60   4.724%   $132.5806   $132.58   $132.60   $132.60  
  Purchase #5 $238.75   3.437%   $246.9558   $246.96   $246.95   $247.00  
  Purchase #6 $219.79   11.821%   $245.7714   $245.77   $245.75   $245.80  
  Purchase #7 $109.81   12.184%   $123.1893   $123.19   $123.20   $123.20  
  7 purchase totals = $1,176.97       $1,271.3655   $1,271.37   $1,271.40   $1,271.50