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 $246.30   8.648%   $267.6   $267.60   $267.60   $267.60  
  Purchase #2 $93.89   6.354%   $99.8558   $99.86   $99.85   $99.90  
  Purchase #3 $208.52   5.537%   $220.0658   $220.07   $220.05   $220.10  
  Purchase #4 $26.54   9.865%   $29.1582   $29.16   $29.15   $29.20  
  Purchase #5 $142.77   12.404%   $160.4792   $160.48   $160.50   $160.50  
  Purchase #6 $232.60   4.814%   $243.7974   $243.80   $243.80   $243.80  
  Purchase #7 $165.32   10.704%   $183.0159   $183.02   $183.00   $183.00  
  7 purchase totals = $1,115.94       $1,203.9723   $1,203.99   $1,203.95   $1,204.10