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 $57.28   10.535%   $63.3144   $63.31   $63.30   $63.30  
  Purchase #2 $243.44   5.507%   $256.8462   $256.85   $256.85   $256.80  
  Purchase #3 $18.29   11.264%   $20.3502   $20.35   $20.35   $20.40  
  Purchase #4 $222.36   9.844%   $244.2491   $244.25   $244.25   $244.20  
  Purchase #5 $218.36   7.769%   $235.3244   $235.32   $235.30   $235.30  
  Purchase #6 $232.95   6.547%   $248.2012   $248.20   $248.20   $248.20  
  Purchase #7 $33.59   4.788%   $35.1983   $35.20   $35.20   $35.20  
  7 purchase totals = $1,026.27       $1,103.4838   $1,103.48   $1,103.45   $1,103.40