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 $230.99   11.471%   $257.4869   $257.49   $257.50   $257.50  
  Purchase #2 $223.74   8.474%   $242.6997   $242.70   $242.70   $242.70  
  Purchase #3 $215.42   5.255%   $226.7403   $226.74   $226.75   $226.70  
  Purchase #4 $155.86   7.734%   $167.9142   $167.91   $167.90   $167.90  
  Purchase #5 $34.39   10.147%   $37.8796   $37.88   $37.90   $37.90  
  Purchase #6 $23.25   11.753%   $25.9826   $25.98   $26.00   $26.00  
  Purchase #7 $75.56   9.479%   $82.7223   $82.72   $82.70   $82.70  
  7 purchase totals = $959.21       $1,041.4256   $1,041.42   $1,041.45   $1,041.40