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 $119.78   12.685%   $134.9741   $134.97   $134.95   $135.00  
  Purchase #2 $154.84   13.443%   $175.6551   $175.66   $175.65   $175.70  
  Purchase #3 $170.48   8.719%   $185.3442   $185.34   $185.35   $185.30  
  Purchase #4 $61.80   8.170%   $66.8491   $66.85   $66.85   $66.80  
  Purchase #5 $70.66   5.415%   $74.4862   $74.49   $74.50   $74.50  
  Purchase #6 $226.68   9.724%   $248.7224   $248.72   $248.70   $248.70  
  Purchase #7 $150.79   8.179%   $163.1231   $163.12   $163.10   $163.10  
  7 purchase totals = $955.03       $1,049.1542   $1,049.15   $1,049.10   $1,049.10