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 $248.62   6.482%   $264.7355   $264.74   $264.75   $264.70  
  Purchase #2 $211.69   10.852%   $234.6626   $234.66   $234.65   $234.70  
  Purchase #3 $155.74   10.638%   $172.3076   $172.31   $172.30   $172.30  
  Purchase #4 $222.48   6.794%   $237.5953   $237.60   $237.60   $237.60  
  Purchase #5 $111.57   10.264%   $123.0215   $123.02   $123.00   $123.00  
  Purchase #6 $50.92   5.666%   $53.8051   $53.81   $53.80   $53.80  
  Purchase #7 $127.91   8.661%   $138.9883   $138.99   $139.00   $139.00  
  7 purchase totals = $1,128.93       $1,225.1159   $1,225.13   $1,225.10   $1,225.10