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 $58.86   5.811%   $62.2804   $62.28   $62.30   $62.30  
  Purchase #2 $30.98   8.171%   $33.5114   $33.51   $33.50   $33.50  
  Purchase #3 $192.99   9.327%   $210.9902   $210.99   $211.00   $211.00  
  Purchase #4 $172.35   12.316%   $193.5766   $193.58   $193.60   $193.60  
  Purchase #5 $67.83   4.832%   $71.1075   $71.11   $71.10   $71.10  
  Purchase #6 $241.31   4.409%   $251.9494   $251.95   $251.95   $251.90  
  Purchase #7 $188.32   7.438%   $202.3272   $202.33   $202.35   $202.30  
  7 purchase totals = $952.64       $1,025.7427   $1,025.75   $1,025.80   $1,025.70