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 $83.68   8.696%   $90.9568   $90.96   $90.95   $91.00  
  Purchase #2 $100.33   8.365%   $108.7226   $108.72   $108.70   $108.70  
  Purchase #3 $246.79   9.325%   $269.8032   $269.80   $269.80   $269.80  
  Purchase #4 $241.76   8.591%   $262.5296   $262.53   $262.55   $262.50  
  Purchase #5 $163.46   11.185%   $181.743   $181.74   $181.75   $181.70  
  Purchase #6 $176.60   5.724%   $186.7086   $186.71   $186.70   $186.70  
  Purchase #7 $93.68   11.810%   $104.7436   $104.74   $104.75   $104.70  
  7 purchase totals = $1,106.30       $1,205.2074   $1,205.20   $1,205.20   $1,205.10