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 $227.70   11.710%   $254.3637   $254.36   $254.35   $254.40  
  Purchase #2 $86.32   7.340%   $92.6559   $92.66   $92.65   $92.70  
  Purchase #3 $105.85   13.834%   $120.4933   $120.49   $120.50   $120.50  
  Purchase #4 $63.78   9.572%   $69.885   $69.89   $69.90   $69.90  
  Purchase #5 $108.67   6.841%   $116.1041   $116.10   $116.10   $116.10  
  Purchase #6 $70.34   12.772%   $79.3238   $79.32   $79.30   $79.30  
  Purchase #7 $39.60   5.245%   $41.677   $41.68   $41.70   $41.70  
  7 purchase totals = $702.26       $774.5028   $774.50   $774.50   $774.60