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 $92.75   7.458%   $99.6673   $99.67   $99.65   $99.70  
  Purchase #2 $236.36   8.134%   $255.5855   $255.59   $255.60   $255.60  
  Purchase #3 $150.61   8.357%   $163.1965   $163.20   $163.20   $163.20  
  Purchase #4 $123.34   4.553%   $128.9557   $128.96   $128.95   $129.00  
  Purchase #5 $220.86   9.238%   $241.263   $241.26   $241.25   $241.30  
  Purchase #6 $178.32   13.836%   $202.9924   $202.99   $203.00   $203.00  
  Purchase #7 $22.42   9.273%   $24.499   $24.50   $24.50   $24.50  
  7 purchase totals = $1,024.66       $1,116.1594   $1,116.17   $1,116.15   $1,116.30