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 $201.36   6.270%   $213.9853   $213.99   $214.00   $214.00  
  Purchase #2 $22.46   8.321%   $24.3289   $24.33   $24.35   $24.30  
  Purchase #3 $132.61   4.439%   $138.4966   $138.50   $138.50   $138.50  
  Purchase #4 $75.48   9.205%   $82.4279   $82.43   $82.45   $82.40  
  Purchase #5 $214.83   12.395%   $241.4582   $241.46   $241.45   $241.50  
  Purchase #6 $45.80   11.259%   $50.9566   $50.96   $50.95   $51.00  
  Purchase #7 $76.81   6.156%   $81.5384   $81.54   $81.55   $81.50  
  7 purchase totals = $769.35       $833.1919   $833.21   $833.25   $833.20