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 $60.59   12.823%   $68.3595   $68.36   $68.35   $68.40  
  Purchase #2 $68.94   8.815%   $75.0171   $75.02   $75.00   $75.00  
  Purchase #3 $5.76   9.585%   $6.3121   $6.31   $6.30   $6.30  
  Purchase #4 $238.36   10.113%   $262.4653   $262.47   $262.45   $262.50  
  Purchase #5 $55.37   11.261%   $61.6052   $61.61   $61.60   $61.60  
  Purchase #6 $146.61   3.871%   $152.2853   $152.29   $152.30   $152.30  
  Purchase #7 $155.58   5.235%   $163.7246   $163.72   $163.70   $163.70  
  7 purchase totals = $731.21       $789.7691   $789.78   $789.70   $789.80