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 $39.93   5.836%   $42.2603   $42.26   $42.25   $42.30  
  Purchase #2 $223.27   13.454%   $253.3087   $253.31   $253.30   $253.30  
  Purchase #3 $231.89   8.386%   $251.3363   $251.34   $251.35   $251.30  
  Purchase #4 $241.78   4.612%   $252.9309   $252.93   $252.95   $252.90  
  Purchase #5 $25.77   6.638%   $27.4806   $27.48   $27.50   $27.50  
  Purchase #6 $201.54   13.242%   $228.2279   $228.23   $228.25   $228.20  
  Purchase #7 $61.59   4.206%   $64.1805   $64.18   $64.20   $64.20  
  7 purchase totals = $1,025.77       $1,119.7252   $1,119.73   $1,119.80   $1,119.70