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 $47.38   13.241%   $53.6536   $53.65   $53.65   $53.70  
  Purchase #2 $32.65   5.822%   $34.5509   $34.55   $34.55   $34.60  
  Purchase #3 $11.53   4.732%   $12.0756   $12.08   $12.10   $12.10  
  Purchase #4 $198.41   3.356%   $205.0686   $205.07   $205.05   $205.10  
  Purchase #5 $206.67   7.128%   $221.4014   $221.40   $221.40   $221.40  
  Purchase #6 $24.76   11.304%   $27.5589   $27.56   $27.55   $27.60  
  Purchase #7 $168.82   12.269%   $189.5325   $189.53   $189.55   $189.50  
  7 purchase totals = $690.22       $743.8415   $743.84   $743.85   $744.00