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 $225.26   9.642%   $246.9796   $246.98   $247.00   $247.00  
  Purchase #2 $184.43   6.781%   $196.9362   $196.94   $196.95   $196.90  
  Purchase #3 $226.53   8.369%   $245.4883   $245.49   $245.50   $245.50  
  Purchase #4 $168.95   7.622%   $181.8274   $181.83   $181.85   $181.80  
  Purchase #5 $118.37   3.416%   $122.4135   $122.41   $122.40   $122.40  
  Purchase #6 $134.47   9.558%   $147.3226   $147.32   $147.30   $147.30  
  Purchase #7 $5.86   6.824%   $6.2599   $6.26   $6.25   $6.30  
  7 purchase totals = $1,063.87       $1,147.2275   $1,147.23   $1,147.25   $1,147.20