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 $140.47   8.564%   $152.4999   $152.50   $152.50   $152.50  
  Purchase #2 $167.67   11.487%   $186.9303   $186.93   $186.95   $186.90  
  Purchase #3 $118.29   4.240%   $123.3055   $123.31   $123.30   $123.30  
  Purchase #4 $153.68   13.522%   $174.4606   $174.46   $174.45   $174.50  
  Purchase #5 $5.26   3.280%   $5.4325   $5.43   $5.45   $5.40  
  Purchase #6 $241.94   11.350%   $269.4002   $269.40   $269.40   $269.40  
  Purchase #7 $31.69   8.519%   $34.3897   $34.39   $34.40   $34.40  
  7 purchase totals = $859.00       $946.4187   $946.42   $946.45   $946.40