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 $56.94   7.625%   $61.2817   $61.28   $61.30   $61.30  
  Purchase #2 $138.74   10.678%   $153.5547   $153.55   $153.55   $153.60  
  Purchase #3 $56.60   7.476%   $60.8314   $60.83   $60.85   $60.80  
  Purchase #4 $31.26   13.769%   $35.5642   $35.56   $35.55   $35.60  
  Purchase #5 $126.69   6.364%   $134.7526   $134.75   $134.75   $134.80  
  Purchase #6 $230.80   10.268%   $254.4985   $254.50   $254.50   $254.50  
  Purchase #7 $74.43   3.163%   $76.7842   $76.78   $76.80   $76.80  
  7 purchase totals = $715.46       $777.2673   $777.25   $777.30   $777.40