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 $33.46   7.297%   $35.9016   $35.90   $35.90   $35.90  
  Purchase #2 $234.61   10.376%   $258.9531   $258.95   $258.95   $259.00  
  Purchase #3 $38.27   3.267%   $39.5203   $39.52   $39.50   $39.50  
  Purchase #4 $85.60   7.727%   $92.2143   $92.21   $92.20   $92.20  
  Purchase #5 $215.45   12.207%   $241.75   $241.75   $241.75   $241.80  
  Purchase #6 $61.36   13.721%   $69.7792   $69.78   $69.80   $69.80  
  Purchase #7 $179.36   9.767%   $196.8781   $196.88   $196.90   $196.90  
  7 purchase totals = $848.11       $934.9966   $934.99   $935.00   $935.10