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 $45.37   8.514%   $49.2328   $49.23   $49.25   $49.20  
  Purchase #2 $206.80   8.733%   $224.8598   $224.86   $224.85   $224.90  
  Purchase #3 $59.45   4.208%   $61.9517   $61.95   $61.95   $62.00  
  Purchase #4 $162.65   8.856%   $177.0543   $177.05   $177.05   $177.10  
  Purchase #5 $105.26   13.265%   $119.2227   $119.22   $119.20   $119.20  
  Purchase #6 $77.40   3.320%   $79.9697   $79.97   $79.95   $80.00  
  Purchase #7 $41.52   5.838%   $43.9439   $43.94   $43.95   $43.90  
  7 purchase totals = $698.45       $756.2349   $756.22   $756.20   $756.30