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 $59.45   13.773%   $67.638   $67.64   $67.65   $67.60  
  Purchase #2 $243.95   8.860%   $265.564   $265.56   $265.55   $265.60  
  Purchase #3 $111.40   9.605%   $122.1   $122.10   $122.10   $122.10  
  Purchase #4 $246.50   5.222%   $259.3722   $259.37   $259.35   $259.40  
  Purchase #5 $131.90   4.440%   $137.7564   $137.76   $137.75   $137.80  
  Purchase #6 $25.46   10.162%   $28.0472   $28.05   $28.05   $28.00  
  Purchase #7 $80.74   7.805%   $87.0418   $87.04   $87.05   $87.00  
  7 purchase totals = $899.40       $967.5196   $967.52   $967.50   $967.50