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 $31.49   8.279%   $34.0971   $34.10   $34.10   $34.10  
  Purchase #2 $229.71   13.416%   $260.5279   $260.53   $260.55   $260.50  
  Purchase #3 $54.87   6.135%   $58.2363   $58.24   $58.25   $58.20  
  Purchase #4 $110.27   12.851%   $124.4408   $124.44   $124.45   $124.40  
  Purchase #5 $117.95   5.254%   $124.1471   $124.15   $124.15   $124.10  
  Purchase #6 $109.46   13.726%   $124.4845   $124.48   $124.50   $124.50  
  Purchase #7 $52.79   13.685%   $60.0143   $60.01   $60.00   $60.00  
  7 purchase totals = $706.54       $785.9480   $785.95   $786.00   $785.80