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 $129.98   8.644%   $141.2155   $141.22   $141.20   $141.20  
  Purchase #2 $214.37   13.663%   $243.6594   $243.66   $243.65   $243.70  
  Purchase #3 $33.48   4.396%   $34.9518   $34.95   $34.95   $35.00  
  Purchase #4 $108.25   4.666%   $113.3009   $113.30   $113.30   $113.30  
  Purchase #5 $234.99   13.865%   $267.5714   $267.57   $267.55   $267.60  
  Purchase #6 $187.29   4.742%   $196.1713   $196.17   $196.15   $196.20  
  Purchase #7 $142.68   3.653%   $147.8921   $147.89   $147.90   $147.90  
  7 purchase totals = $1,051.04       $1,144.7624   $1,144.76   $1,144.70   $1,144.90