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 $52.27   12.171%   $58.6318   $58.63   $58.65   $58.60  
  Purchase #2 $248.50   11.473%   $277.0104   $277.01   $277.00   $277.00  
  Purchase #3 $155.79   5.145%   $163.8054   $163.81   $163.80   $163.80  
  Purchase #4 $83.41   6.268%   $88.6381   $88.64   $88.65   $88.60  
  Purchase #5 $41.74   11.747%   $46.6432   $46.64   $46.65   $46.60  
  Purchase #6 $211.99   7.305%   $227.4759   $227.48   $227.50   $227.50  
  Purchase #7 $230.45   10.190%   $253.9329   $253.93   $253.95   $253.90  
  7 purchase totals = $1,024.15       $1,116.1377   $1,116.14   $1,116.20   $1,116.00