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 $184.47   8.273%   $199.7312   $199.73   $199.75   $199.70  
  Purchase #2 $27.92   3.730%   $28.9614   $28.96   $28.95   $29.00  
  Purchase #3 $147.99   9.600%   $162.197   $162.20   $162.20   $162.20  
  Purchase #4 $43.78   5.853%   $46.3424   $46.34   $46.35   $46.30  
  Purchase #5 $103.50   4.783%   $108.4504   $108.45   $108.45   $108.50  
  Purchase #6 $58.79   4.850%   $61.6413   $61.64   $61.65   $61.60  
  Purchase #7 $143.46   7.519%   $154.2468   $154.25   $154.25   $154.20  
  7 purchase totals = $709.91       $761.5705   $761.57   $761.60   $761.50