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 $188.98   13.354%   $214.2164   $214.22   $214.20   $214.20  
  Purchase #2 $173.67   4.357%   $181.2368   $181.24   $181.25   $181.20  
  Purchase #3 $239.41   11.581%   $267.1361   $267.14   $267.15   $267.10  
  Purchase #4 $199.37   10.801%   $220.904   $220.90   $220.90   $220.90  
  Purchase #5 $116.85   4.319%   $121.8968   $121.90   $121.90   $121.90  
  Purchase #6 $239.63   13.357%   $271.6374   $271.64   $271.65   $271.60  
  Purchase #7 $205.85   12.354%   $231.2807   $231.28   $231.30   $231.30  
  7 purchase totals = $1,363.76       $1,508.3082   $1,508.32   $1,508.35   $1,508.20