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 $67.93   8.342%   $73.5967   $73.60   $73.60   $73.60  
  Purchase #2 $33.59   3.759%   $34.8526   $34.85   $34.85   $34.90  
  Purchase #3 $174.76   8.582%   $189.7579   $189.76   $189.75   $189.80  
  Purchase #4 $61.97   8.547%   $67.2666   $67.27   $67.25   $67.30  
  Purchase #5 $22.25   12.708%   $25.0775   $25.08   $25.10   $25.10  
  Purchase #6 $226.34   8.735%   $246.1108   $246.11   $246.10   $246.10  
  Purchase #7 $174.86   7.167%   $187.3922   $187.39   $187.40   $187.40  
  7 purchase totals = $761.70       $824.0543   $824.06   $824.05   $824.20