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 $79.58   6.846%   $85.028   $85.03   $85.05   $85.00  
  Purchase #2 $137.68   4.413%   $143.7558   $143.76   $143.75   $143.80  
  Purchase #3 $23.25   6.165%   $24.6834   $24.68   $24.70   $24.70  
  Purchase #4 $160.59   9.149%   $175.2824   $175.28   $175.30   $175.30  
  Purchase #5 $236.55   12.447%   $265.9934   $265.99   $266.00   $266.00  
  Purchase #6 $190.78   7.124%   $204.3712   $204.37   $204.35   $204.40  
  Purchase #7 $84.72   8.595%   $92.0017   $92.00   $92.00   $92.00  
  7 purchase totals = $913.15       $991.1159   $991.11   $991.15   $991.20