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 $65.75   3.774%   $68.2314   $68.23   $68.25   $68.20  
  Purchase #2 $176.50   10.127%   $194.3742   $194.37   $194.35   $194.40  
  Purchase #3 $182.44   7.617%   $196.3365   $196.34   $196.35   $196.30  
  Purchase #4 $226.43   6.485%   $241.114   $241.11   $241.10   $241.10  
  Purchase #5 $150.70   9.541%   $165.0783   $165.08   $165.10   $165.10  
  Purchase #6 $5.91   13.621%   $6.715   $6.72   $6.70   $6.70  
  Purchase #7 $111.48   13.477%   $126.5042   $126.50   $126.50   $126.50  
  7 purchase totals = $919.21       $998.3536   $998.35   $998.35   $998.30