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 $219.58   12.108%   $246.1667   $246.17   $246.15   $246.20  
  Purchase #2 $62.51   9.606%   $68.5147   $68.51   $68.50   $68.50  
  Purchase #3 $120.75   5.810%   $127.7656   $127.77   $127.75   $127.80  
  Purchase #4 $29.47   12.362%   $33.1131   $33.11   $33.10   $33.10  
  Purchase #5 $214.63   13.119%   $242.7873   $242.79   $242.80   $242.80  
  Purchase #6 $150.60   12.440%   $169.3346   $169.33   $169.35   $169.30  
  Purchase #7 $112.95   5.277%   $118.9104   $118.91   $118.90   $118.90  
  7 purchase totals = $910.49       $1,006.5924   $1,006.59   $1,006.55   $1,006.60