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 $221.94   13.656%   $252.2481   $252.25   $252.25   $252.20  
  Purchase #2 $74.86   12.109%   $83.9248   $83.92   $83.90   $83.90  
  Purchase #3 $219.35   7.466%   $235.7267   $235.73   $235.75   $235.70  
  Purchase #4 $172.81   10.522%   $190.9931   $190.99   $191.00   $191.00  
  Purchase #5 $198.86   6.174%   $211.1376   $211.14   $211.15   $211.10  
  Purchase #6 $237.99   7.457%   $255.7369   $255.74   $255.75   $255.70  
  Purchase #7 $163.31   5.729%   $172.666   $172.67   $172.65   $172.70  
  7 purchase totals = $1,289.12       $1,402.4332   $1,402.44   $1,402.45   $1,402.30