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 $87.84   12.227%   $98.5802   $98.58   $98.60   $98.60  
  Purchase #2 $208.60   6.425%   $222.0026   $222.00   $222.00   $222.00  
  Purchase #3 $145.79   10.380%   $160.923   $160.92   $160.90   $160.90  
  Purchase #4 $196.73   5.159%   $206.8793   $206.88   $206.90   $206.90  
  Purchase #5 $53.55   12.424%   $60.2031   $60.20   $60.20   $60.20  
  Purchase #6 $114.45   8.163%   $123.7926   $123.79   $123.80   $123.80  
  Purchase #7 $167.64   3.607%   $173.6868   $173.69   $173.70   $173.70  
  7 purchase totals = $974.60       $1,046.0676   $1,046.06   $1,046.10   $1,046.10