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 $56.34   5.581%   $59.4843   $59.48   $59.50   $59.50  
  Purchase #2 $232.48   5.798%   $245.9592   $245.96   $245.95   $246.00  
  Purchase #3 $94.91   4.566%   $99.2436   $99.24   $99.25   $99.20  
  Purchase #4 $65.98   5.805%   $69.8101   $69.81   $69.80   $69.80  
  Purchase #5 $77.81   13.357%   $88.2031   $88.20   $88.20   $88.20  
  Purchase #6 $224.63   10.253%   $247.6613   $247.66   $247.65   $247.70  
  Purchase #7 $65.77   3.718%   $68.2153   $68.22   $68.20   $68.20  
  7 purchase totals = $817.92       $878.5769   $878.57   $878.55   $878.60