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 $214.28   11.293%   $238.4786   $238.48   $238.50   $238.50  
  Purchase #2 $120.49   11.413%   $134.2415   $134.24   $134.25   $134.20  
  Purchase #3 $49.64   6.566%   $52.8994   $52.90   $52.90   $52.90  
  Purchase #4 $204.37   12.483%   $229.8815   $229.88   $229.90   $229.90  
  Purchase #5 $183.53   12.357%   $206.2088   $206.21   $206.20   $206.20  
  Purchase #6 $165.92   4.873%   $174.0053   $174.01   $174.00   $174.00  
  Purchase #7 $76.92   6.801%   $82.1513   $82.15   $82.15   $82.20  
  7 purchase totals = $1,015.15       $1,117.8664   $1,117.87   $1,117.90   $1,117.90