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 $55.60   13.336%   $63.0148   $63.01   $63.00   $63.00  
  Purchase #2 $225.82   12.594%   $254.2598   $254.26   $254.25   $254.30  
  Purchase #3 $87.88   5.311%   $92.5473   $92.55   $92.55   $92.50  
  Purchase #4 $95.32   13.641%   $108.3226   $108.32   $108.30   $108.30  
  Purchase #5 $188.63   8.222%   $204.1392   $204.14   $204.15   $204.10  
  Purchase #6 $118.69   11.760%   $132.6479   $132.65   $132.65   $132.60  
  Purchase #7 $158.71   5.314%   $167.1438   $167.14   $167.15   $167.10  
  7 purchase totals = $930.65       $1,022.0754   $1,022.07   $1,022.05   $1,021.90