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 $160.46   10.742%   $177.6966   $177.70   $177.70   $177.70  
  Purchase #2 $136.95   13.622%   $155.6053   $155.61   $155.60   $155.60  
  Purchase #3 $22.88   8.362%   $24.7932   $24.79   $24.80   $24.80  
  Purchase #4 $104.42   4.735%   $109.3643   $109.36   $109.35   $109.40  
  Purchase #5 $245.55   12.279%   $275.7011   $275.70   $275.70   $275.70  
  Purchase #6 $220.91   13.603%   $250.9604   $250.96   $250.95   $251.00  
  Purchase #7 $86.82   7.183%   $93.0563   $93.06   $93.05   $93.10  
  7 purchase totals = $977.99       $1,087.1772   $1,087.18   $1,087.15   $1,087.30