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 $208.66   11.427%   $232.5036   $232.50   $232.50   $232.50  
  Purchase #2 $48.35   7.462%   $51.9579   $51.96   $51.95   $52.00  
  Purchase #3 $145.63   13.661%   $165.5245   $165.52   $165.50   $165.50  
  Purchase #4 $74.30   10.188%   $81.8697   $81.87   $81.85   $81.90  
  Purchase #5 $87.60   7.321%   $94.0132   $94.01   $94.00   $94.00  
  Purchase #6 $170.46   7.547%   $183.3246   $183.32   $183.30   $183.30  
  Purchase #7 $82.79   7.844%   $89.284   $89.28   $89.30   $89.30  
  7 purchase totals = $817.79       $898.4775   $898.46   $898.40   $898.50